ON PERFECT and NEAR-PERFECT NUMBERS 1. Introduction a Perfect
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1 Mersenne Primes and Perfect Numbers
1 Mersenne Primes and Perfect Numbers Basic idea: try to construct primes of the form an − 1; a, n ≥ 1. e.g., 21 − 1 = 3 but 24 − 1=3· 5 23 − 1=7 25 − 1=31 26 − 1=63=32 · 7 27 − 1 = 127 211 − 1 = 2047 = (23)(89) 213 − 1 = 8191 Lemma: xn − 1=(x − 1)(xn−1 + xn−2 + ···+ x +1) Corollary:(x − 1)|(xn − 1) So for an − 1tobeprime,weneeda =2. Moreover, if n = md, we can apply the lemma with x = ad.Then (ad − 1)|(an − 1) So we get the following Lemma If an − 1 is a prime, then a =2andn is prime. Definition:AMersenne prime is a prime of the form q =2p − 1,pprime. Question: are they infinitely many Mersenne primes? Best known: The 37th Mersenne prime q is associated to p = 3021377, and this was done in 1998. One expects that p = 6972593 will give the next Mersenne prime; this is close to being proved, but not all the details have been checked. Definition: A positive integer n is perfect iff it equals the sum of all its (positive) divisors <n. Definition: σ(n)= d|n d (divisor function) So u is perfect if n = σ(u) − n, i.e. if σ(u)=2n. Well known example: n =6=1+2+3 Properties of σ: 1. σ(1) = 1 1 2. n is a prime iff σ(n)=n +1 p σ pj p ··· pj pj+1−1 3. If is a prime, ( )=1+ + + = p−1 4. (Exercise) If (n1,n2)=1thenσ(n1)σ(n2)=σ(n1n2) “multiplicativity”. -
Bi-Unitary Multiperfect Numbers, I
Notes on Number Theory and Discrete Mathematics Print ISSN 1310–5132, Online ISSN 2367–8275 Vol. 26, 2020, No. 1, 93–171 DOI: 10.7546/nntdm.2020.26.1.93-171 Bi-unitary multiperfect numbers, I Pentti Haukkanen1 and Varanasi Sitaramaiah2 1 Faculty of Information Technology and Communication Sciences, FI-33014 Tampere University, Finland e-mail: [email protected] 2 1/194e, Poola Subbaiah Street, Taluk Office Road, Markapur Prakasam District, Andhra Pradesh, 523316 India e-mail: [email protected] Dedicated to the memory of Prof. D. Suryanarayana Received: 19 December 2019 Revised: 21 January 2020 Accepted: 5 March 2020 Abstract: A divisor d of a positive integer n is called a unitary divisor if gcd(d; n=d) = 1; and d is called a bi-unitary divisor of n if the greatest common unitary divisor of d and n=d is unity. The concept of a bi-unitary divisor is due to D. Surynarayana [12]. Let σ∗∗(n) denote the sum of the bi-unitary divisors of n: A positive integer n is called a bi-unitary perfect number if σ∗∗(n) = 2n. This concept was introduced by C. R. Wall in 1972 [15], and he proved that there are only three bi-unitary perfect numbers, namely 6, 60 and 90. In 1987, Peter Hagis [6] introduced the notion of bi-unitary multi k-perfect numbers as solu- tions n of the equation σ∗∗(n) = kn. A bi-unitary multi 3-perfect number is called a bi-unitary triperfect number. A bi-unitary multiperfect number means a bi-unitary multi k-perfect number with k ≥ 3: Hagis [6] proved that there are no odd bi-unitary multiperfect numbers. -
Prime Divisors in the Rationality Condition for Odd Perfect Numbers
Aid#59330/Preprints/2019-09-10/www.mathjobs.org RFSC 04-01 Revised The Prime Divisors in the Rationality Condition for Odd Perfect Numbers Simon Davis Research Foundation of Southern California 8861 Villa La Jolla Drive #13595 La Jolla, CA 92037 Abstract. It is sufficient to prove that there is an excess of prime factors in the product of repunits with odd prime bases defined by the sum of divisors of the integer N = (4k + 4m+1 ℓ 2αi 1) i=1 qi to establish that there do not exist any odd integers with equality (4k+1)4m+2−1 between σ(N) and 2N. The existence of distinct prime divisors in the repunits 4k , 2α +1 Q q i −1 i , i = 1,...,ℓ, in σ(N) follows from a theorem on the primitive divisors of the Lucas qi−1 sequences and the square root of the product of 2(4k + 1), and the sequence of repunits will not be rational unless the primes are matched. Minimization of the number of prime divisors in σ(N) yields an infinite set of repunits of increasing magnitude or prime equations with no integer solutions. MSC: 11D61, 11K65 Keywords: prime divisors, rationality condition 1. Introduction While even perfect numbers were known to be given by 2p−1(2p − 1), for 2p − 1 prime, the universality of this result led to the the problem of characterizing any other possible types of perfect numbers. It was suggested initially by Descartes that it was not likely that odd integers could be perfect numbers [13]. After the work of de Bessy [3], Euler proved σ(N) that the condition = 2, where σ(N) = d|N d is the sum-of-divisors function, N d integer 4m+1 2α1 2αℓ restricted odd integers to have the form (4kP+ 1) q1 ...qℓ , with 4k + 1, q1,...,qℓ prime [18], and further, that there might exist no set of prime bases such that the perfect number condition was satisfied. -
On Perfect and Multiply Perfect Numbers
On perfect and multiply perfect numbers . by P. ERDÖS, (in Haifa . Israel) . Summary. - Denote by P(x) the number o f integers n ~_ x satisfying o(n) -- 0 (mod n.), and by P2 (x) the number of integers nix satisfying o(n)-2n . The author proves that P(x) < x'314:4- and P2 (x) < x(t-c)P for a certain c > 0 . Denote by a(n) the sum of the divisors of n, a(n) - E d. A number n din is said to be perfect if a(n) =2n, and it is said to be multiply perfect if o(n) - kn for some integer k . Perfect numbers have been studied since antiquity. l t is contained in the books of EUCLID that every number of the form 2P- ' ( 2P - 1) where both p and 2P - 1 are primes is perfect . EULER (1) proved that every even perfect number is of the above form . It is not known if there are infinitely many even perfect numbers since it is not known if there are infinitely many primes of the form 2P - 1. Recently the electronic computer of the Institute for Numerical Analysis the S .W.A .C . determined all primes of the form 20 - 1 for p < 2300. The largest prime found was 2J9 "' - 1, which is the largest prime known at present . It is not known if there are an odd perfect numbers . EULER (') proved that all odd perfect numbers are of the form (1) pam2, p - x - 1 (mod 4), and SYLVESTER (') showed that an odd perfect number must have at least five distinct prime factors . -
Unit 6: Multiply & Divide Fractions Key Words to Know
Unit 6: Multiply & Divide Fractions Learning Targets: LT 1: Interpret a fraction as division of the numerator by the denominator (a/b = a ÷ b) LT 2: Solve word problems involving division of whole numbers leading to answers in the form of fractions or mixed numbers, e.g. by using visual fraction models or equations to represent the problem. LT 3: Apply and extend previous understanding of multiplication to multiply a fraction or whole number by a fraction. LT 4: Interpret the product (a/b) q ÷ b. LT 5: Use a visual fraction model. Conversation Starters: Key Words § How are fractions like division problems? (for to Know example: If 9 people want to shar a 50-lb *Fraction sack of rice equally by *Numerator weight, how many pounds *Denominator of rice should each *Mixed number *Improper fraction person get?) *Product § 3 pizzas at 10 slices each *Equation need to be divided by 14 *Division friends. How many pieces would each friend receive? § How can a model help us make sense of a problem? Fractions as Division Students will interpret a fraction as division of the numerator by the { denominator. } What does a fraction as division look like? How can I support this Important Steps strategy at home? - Frac&ons are another way to Practice show division. https://www.khanacademy.org/math/cc- - Fractions are equal size pieces of a fifth-grade-math/cc-5th-fractions-topic/ whole. tcc-5th-fractions-as-division/v/fractions- - The numerator becomes the as-division dividend and the denominator becomes the divisor. Quotient as a Fraction Students will solve real world problems by dividing whole numbers that have a quotient resulting in a fraction. -
Arxiv:1412.5226V1 [Math.NT] 16 Dec 2014 Hoe 11
q-PSEUDOPRIMALITY: A NATURAL GENERALIZATION OF STRONG PSEUDOPRIMALITY JOHN H. CASTILLO, GILBERTO GARC´IA-PULGAR´IN, AND JUAN MIGUEL VELASQUEZ-SOTO´ Abstract. In this work we present a natural generalization of strong pseudoprime to base b, which we have called q-pseudoprime to base b. It allows us to present another way to define a Midy’s number to base b (overpseudoprime to base b). Besides, we count the bases b such that N is a q-probable prime base b and those ones such that N is a Midy’s number to base b. Furthemore, we prove that there is not a concept analogous to Carmichael numbers to q-probable prime to base b as with the concept of strong pseudoprimes to base b. 1. Introduction Recently, Grau et al. [7] gave a generalization of Pocklignton’s Theorem (also known as Proth’s Theorem) and Miller-Rabin primality test, it takes as reference some works of Berrizbeitia, [1, 2], where it is presented an extension to the concept of strong pseudoprime, called ω-primes. As Grau et al. said it is right, but its application is not too good because it is needed m-th primitive roots of unity, see [7, 12]. In [7], it is defined when an integer N is a p-strong probable prime base a, for p a prime divisor of N −1 and gcd(a, N) = 1. In a reading of that paper, we discovered that if a number N is a p-strong probable prime to base 2 for each p prime divisor of N − 1, it is actually a Midy’s number or a overpseu- doprime number to base 2. -
MORE-ON-SEMIPRIMES.Pdf
MORE ON FACTORING SEMI-PRIMES In the last few years I have spent some time examining prime numbers and their properties. Among some of my new results are the a Prime Number Function F(N) and the concept of Number Fraction f(N). We can define these quantities as – (N ) N 1 f (N 2 ) 1 f (N ) and F(N ) N Nf (N 3 ) Here (N) is the divisor function of number theory. The interesting property of these functions is that when N is a prime then f(N)=0 and F(N)=1. For composite numbers f(N) is a positive fraction and F(N) will be less than one. One of the problems of major practical interest in number theory is how to rapidly factor large semi-primes N=pq, where p and q are prime numbers. This interest stems from the fact that encoded messages using public keys are vulnerable to decoding by adversaries if they can factor large semi-primes when they have a digit length of the order of 100. We want here to show how one might attempt to factor such large primes by a brute force approach using the above f(N) function. Our starting point is to consider a large semi-prime given by- N=pq with p<sqrt(N)<q By the basic definition of f(N) we get- p q p2 N f (N ) f ( pq) N pN This may be written as a quadratic in p which reads- p2 pNf (N ) N 0 It has the solution- p K K 2 N , with p N Here K=Nf(N)/2={(N)-N-1}/2. -
NOTES on CARTIER and WEIL DIVISORS Recall: Definition 0.1. A
NOTES ON CARTIER AND WEIL DIVISORS AKHIL MATHEW Abstract. These are notes on divisors from Ravi Vakil's book [2] on scheme theory that I prepared for the Foundations of Algebraic Geometry seminar at Harvard. Most of it is a rewrite of chapter 15 in Vakil's book, and the originality of these notes lies in the mistakes. I learned some of this from [1] though. Recall: Definition 0.1. A line bundle on a ringed space X (e.g. a scheme) is a locally free sheaf of rank one. The group of isomorphism classes of line bundles is called the Picard group and is denoted Pic(X). Here is a standard source of line bundles. 1. The twisting sheaf 1.1. Twisting in general. Let R be a graded ring, R = R0 ⊕ R1 ⊕ ::: . We have discussed the construction of the scheme ProjR. Let us now briefly explain the following additional construction (which will be covered in more detail tomorrow). L Let M = Mn be a graded R-module. Definition 1.1. We define the sheaf Mf on ProjR as follows. On the basic open set D(f) = SpecR(f) ⊂ ProjR, we consider the sheaf associated to the R(f)-module M(f). It can be checked easily that these sheaves glue on D(f) \ D(g) = D(fg) and become a quasi-coherent sheaf Mf on ProjR. Clearly, the association M ! Mf is a functor from graded R-modules to quasi- coherent sheaves on ProjR. (For R reasonable, it is in fact essentially an equiva- lence, though we shall not need this.) We now set a bit of notation. -
+P.+1 P? '" PT Hence
1907.] MULTIPLY PEKFECT NUMBERS. 383 A TABLE OF MULTIPLY PERFECT NUMBERS. BY PEOFESSOR R. D. CARMICHAEL. (Read before the American Mathematical Society, February 23, 1907.) A MULTIPLY perfect number is one which is an exact divisor of the sum of all its divisors, the quotient being the multiplicity.* The object of this paper is to exhibit a method for determining all such numbers up to 1,000,000,000 and to give a complete table of them. I include an additional table giving such other numbers as are known to me to be multiply perfect. Let the number N, of multiplicity m (m> 1), be of the form where pv p2, • • •, pn are different primes. Then by definition and by the formula for the sum of the factors of a number, we have +P? -1+---+p + ~L pi" + Pi»'1 + • • (l)m=^- 1 •+P.+1 p? '" PT Hence (2) Pi~l Pa"1 Pn-1 These formulas will be of frequent use throughout the paper. Since 2•3•5•7•11•13•17•19•23 = 223,092,870, multiply perfect numbers less than 1,000,000,000 contain not more than nine different prime factors ; such numbers, lacking the factor 2, contain not more than eight different primes ; and, lacking the factors 2 and 3, they contain not more than seven different primes. First consider the case in which N does not contain either 2 or 3 as a factor. By equation (2) we have (^\ «M ^ 6 . 7 . 11 . 1£. 11 . 19 .2ft « 676089 [Ö) m<ï*6 TTT if 16 ï¥ ïî — -BTÏTT6- Hence m=2 ; moreover seven primes are necessary to this value. -
PRIME-PERFECT NUMBERS Paul Pollack [email protected] Carl
PRIME-PERFECT NUMBERS Paul Pollack Department of Mathematics, University of Illinois, Urbana, Illinois 61801, USA [email protected] Carl Pomerance Department of Mathematics, Dartmouth College, Hanover, New Hampshire 03755, USA [email protected] In memory of John Lewis Selfridge Abstract We discuss a relative of the perfect numbers for which it is possible to prove that there are infinitely many examples. Call a natural number n prime-perfect if n and σ(n) share the same set of distinct prime divisors. For example, all even perfect numbers are prime-perfect. We show that the count Nσ(x) of prime-perfect numbers in [1; x] satisfies estimates of the form c= log log log x 1 +o(1) exp((log x) ) ≤ Nσ(x) ≤ x 3 ; as x ! 1. We also discuss the analogous problem for the Euler function. Letting N'(x) denote the number of n ≤ x for which n and '(n) share the same set of prime factors, we show that as x ! 1, x1=2 x7=20 ≤ N (x) ≤ ; where L(x) = xlog log log x= log log x: ' L(x)1=4+o(1) We conclude by discussing some related problems posed by Harborth and Cohen. 1. Introduction P Let σ(n) := djn d be the sum of the proper divisors of n. A natural number n is called perfect if σ(n) = 2n and, more generally, multiply perfect if n j σ(n). The study of such numbers has an ancient pedigree (surveyed, e.g., in [5, Chapter 1] and [28, Chapter 1]), but many of the most interesting problems remain unsolved. -
The Distribution of Pseudoprimes
The Distribution of Pseudoprimes Matt Green September, 2002 The RSA crypto-system relies on the availability of very large prime num- bers. Tests for finding these large primes can be categorized as deterministic and probabilistic. Deterministic tests, such as the Sieve of Erastothenes, of- fer a 100 percent assurance that the number tested and passed as prime is actually prime. Despite their refusal to err, deterministic tests are generally not used to find large primes because they are very slow (with the exception of a recently discovered polynomial time algorithm). Probabilistic tests offer a much quicker way to find large primes with only a negligibal amount of error. I have studied a simple, and comparatively to other probabilistic tests, error prone test based on Fermat’s little theorem. Fermat’s little theorem states that if b is a natural number and n a prime then bn−1 ≡ 1 (mod n). To test a number n for primality we pick any natural number less than n and greater than 1 and first see if it is relatively prime to n. If it is, then we use this number as a base b and see if Fermat’s little theorem holds for n and b. If the theorem doesn’t hold, then we know that n is not prime. If the theorem does hold then we can accept n as prime right now, leaving a large chance that we have made an error, or we can test again with a different base. Chances improve that n is prime with every base that passes but for really big numbers it is cumbersome to test all possible bases. -
Some New Results on Odd Perfect Numbers
Pacific Journal of Mathematics SOME NEW RESULTS ON ODD PERFECT NUMBERS G. G. DANDAPAT,JOHN L. HUNSUCKER AND CARL POMERANCE Vol. 57, No. 2 February 1975 PACIFIC JOURNAL OF MATHEMATICS Vol. 57, No. 2, 1975 SOME NEW RESULTS ON ODD PERFECT NUMBERS G. G. DANDAPAT, J. L. HUNSUCKER AND CARL POMERANCE If ra is a multiply perfect number (σ(m) = tm for some integer ί), we ask if there is a prime p with m = pan, (pa, n) = 1, σ(n) = pα, and σ(pa) = tn. We prove that the only multiply perfect numbers with this property are the even perfect numbers and 672. Hence we settle a problem raised by Suryanarayana who asked if odd perfect numbers neces- sarily had such a prime factor. The methods of the proof allow us also to say something about odd solutions to the equation σ(σ(n)) ~ 2n. 1* Introduction* In this paper we answer a question on odd perfect numbers posed by Suryanarayana [17]. It is known that if m is an odd perfect number, then m = pak2 where p is a prime, p Jf k, and p = a z= 1 (mod 4). Suryanarayana asked if it necessarily followed that (1) σ(k2) = pa , σ(pa) = 2k2 . Here, σ is the sum of the divisors function. We answer this question in the negative by showing that no odd perfect number satisfies (1). We actually consider a more general question. If m is multiply perfect (σ(m) = tm for some integer t), we say m has property S if there is a prime p with m = pan, (pa, n) = 1, and the equations (2) σ(n) = pa , σ(pa) = tn hold.