New results on p-Bernoulli numbers Levent Kargın Akseki Vocational School Alanya Alaaddin Keykubat University Antalya TR-07630 Turkey [email protected] Abstract We realize that geometric polynomials and p-Bernoulli polynomials and numbers are closely related with an integral representation. There- fore, using geometric polynomials, we extend some properties of Bernoulli polynomials and numbers such as recurrence relations, telescopic formula and Raabe’s formula to p-Bernoulli polynomials and numbers. In par- ticular cases of these results, we establish some new results for Bernoulli polynomials and numbers. Moreover, we evaluate a Faulhaber-type sum- mation in terms of p-Bernoulli polynomials. 2000 Mathematics Subject Classification: 11B68, 11B83 Key words: p-Bernoulli number, geometric polynomial, finite sum- mation 1 Introduction The Bernoulli polynomials Bn (x) are defined by exponential generating function tn text B (x) = , |t| < 2π. (1) n n! et − 1 ≥0 nX In particular, the rational numbers Bn = Bn (0) are called Bernoulli numbers arXiv:1702.06422v1 [math.NT] 20 Feb 2017 and have an explicit formula [14] n n (−1)k k! B = , n k k +1 =0 kX n where k is the Stirling number of second kind [14]. As it is well known, the Bernoulli numbers are considerable importance in different areas of mathematics such as number theory, combinatorics, special functions. Moreover, many generalizations and extensions of these numbers appear in the literature. One of the generalization of the Bernoulli numbers is 1 p-Bernoulli numbers, defined by a three-term recurrence relation [23] 2 (p + 1) B +1 = pB − B +1, (2) n ,p n,p p +2 n,p with the initial condition B0,p = 1. These numbers also satisfy an explicit formula n p +1 n + p (−1)k (k + p)! B = , n,p p! k + p k + p +1 =0 p Xk where n+p is the p-Stirling number of second kind [6]. k+p p As a special case, setting p = 0 in the above equation gives Bn,0 = Bn. p-Bernoulli polynomials which is the polynomial extension of Bn,p, are de- fined by the following convolution n n B (x)= xn−kB . (3) n,p k k,p =0 Xk The first few p-Bernoulli polynomials are B0,p (x) = 1, 1 B1 (x) = x − , ,p p +2 2 2x p − 1 B2 (x) = x − − . ,p p +2 (p +2)(p + 3) Moreover, these polynomials have integral representations a B +1 (a) − B +1 (b) B (t) dt = n ,p n ,p , (4) n,p n +1 Zb 1 n 1 n +1 B (t) dt = B , (5) n,p n +1 k k,p =0 Z0 kX a recurrence relation −1 n n B (x + 1) − B (x)= B (x) , (6) n,p n,p k k,p =0 Xk and a three-term recurrence relation 2 (p + 1) B +1 (x) = (x + p) B (x) − B +1 (x) . (7) n ,p n,p p +2 n,p In the special case of (3) when x = 0, we obtain Bn,p (0) = Bn,p. Some other properties and applications of p-Bernoulli polynomials and num- bers can be found in [23]. 2 The main formula of this paper is [23, p. 361] 0 1 tn (1 + y)p B = dy, for p ≥ 0. p +1 n,p n! 1 − y (et − 1) ≥0 nX −Z1 Using the generating function of geometric polynomials wn (y) (see Section 2 for details of wn (y)), the above equation can be written as 0 1 B = (1 + y)p w (y) dy (8) p +1 n,p n −Z1 which is the generalization of Keller’s identity [16] 0 wn (y) dy = Bn. −Z1 Thus, using this integral representation and the properties of geometric polyno- mials, we generalize a recurrence relation of Bernoulli numbers to p-Bernoulli numbers and obtain an explicit formula for p-Bernoulli numbers. Moreover, extending the representation (8) to p-Bernoulli polynomials, we give the gener- alization of the telescopic formula and Raabe’s formula of Bernoulli polynomials for p-Bernoulli polynomials. Thus, as special cases of these results, we get an explicit formula, a finite summation and a convolution identity for Bernoulli polynomials and numbers. Besides, we evaluate a Faulhaber-type summation in terms of p-Bernoulli polynomials. First, we extend the well known recurrence relation of Bernoulli numbers n n +1 B =0 for n ≥ 1, k k =0 kX to p-Bernoulli numbers in the following theorem. Theorem 1 For n ≥ 1 and p ≥ 0, n n +1 Bk,p = −pBn,p. (9) =0 k Xk We note that using (5) and (6) in the above theorem gives us the following conclusions Bn,p (1) = Bn,p − pBn−1,p, and 1 −pB B (t) dt = n,p , (10) n,p n +1 Z0 3 respectively. Also, these results are the generalization of the following well known properties of Bn 1 Bn (1) = Bn and Bn (t) dt =0, for n ≥ 1. Z0 The Bernoulli numbers are connected with some well known special numbers [7, 8, 18, 19, 20, 21]. Rahmani [23] also gave explicit formulas involving different kind of special numbers. Now, we obtain a new explicit formula for Bn,p, and hence Bn, in the following theorem. Theorem 2 For n ≥ 1 and p ≥ 0, n + n (−1)k n k! B = (p + 1) . (11) n,p k (k + p) (k + p + 1) =1 Xk When p =0 this becomes n + n (−1)k n (k − 1)! B = . (12) n k k +1 =1 kX In order to deal with some properties of p-Bernoulli polynomials, we need to extend the integral representation (8) to Bn,p (x). Proposition 3 Let n and p be the non-negative integers. Then we have 0 1 B (x)= (1 + y)p w (x; y) dy, (13) p +1 n,p n −Z1 where wn (x; y) (see Section 2) is two variable geometric polynomials. One of the important properties of Bn (x) is the telescopic formula n−1 Bn (x + 1) − Bn (x)= nx . From this formula, Bernoulli gave a closed formula for Faulhaber’s summation in terms of Bernoulli polynomials and numbers m B +1 (m + 1) − B +1 kn = n n . (14) n +1 =0 kX Now, we want to give an extension of telescopic formula for p-Bernoulli polynomials. Proposition 4 For any non-negative integer n and p, p +2 n B +1 (x + 1) − B +1 (x)= (B (x + 1) − x ) . (15) n,p n,p p +1 n,p 4 This telescopic formula for p-Bernoulli polynomials gives us the evaluation of finite summation of p-Bernoulli polynomials. In particular case p = 0, we arrive at a new finite summation involving Bernoulli polynomials. Theorem 5 For any non-negative integer n,m and p, m Bn+1 (m + 1) − Bn+1 p +1 B (k +1)= + (B +1 (m + 1) − B +1) . n,p n +1 p +2 n,p n,p k=0 X (16) When p =0 this becomes m n [Bn (k +1)+ nk ] = (m + 1) Bn (m + 1) . (17) =0 kX Another important identity for Bernoulli polynomials is the Raabe’s formula −1 m k mn−1 B x + = B (mx) . n m n =0 Xk Now, we want to extend the Raabe’s formula to p-Bernoulli polynomials. Theorem 6 For m ≥ 1 and n,p ≥ 0, m−1 n k n mkB (mx) B mn−1 B x + = (p + 1) B (mx) − p n−k k,p . n,p m n k k +1 k=0 k=0 X X (18) Using the generating function technique, Chu and Zhou [9] give several con- volution identities for Bernoulli numbers. Two of them are the followings: n n Bk+1Bn−k = −B − B +1, k k +1 n n =0 kX n k n−1 n 2 B +1B − −Bn+1 − 2 +1 Bn k n k = . k k +1 2 k=0 X If we set p = 1 and x = 0 in (18) and use (2) and (8), we have a close formula for a generalization of the above equations in the following corollary. Corollary 7 For m ≥ 1 and n,p ≥ 0, n k m−1 n m B +1B −mB − B +1 k k k n−k = n n + mn−1 B . k k +1 m m n m =0 =0 Xk Xk Finally, we evaluate a Faulhaber-type summation in terms of p-Bernoulli polynomials and numbers which generalize the following finite summation [15, p. 18, Eq. 1] n k (−1) n +1 n n = ((−1) + 1) . =0 k n +2 Xk 5 Theorem 8 For n ≥ 1 and p ≥ 0, we have n p k k (−1) n +1 n+p n = (−1) Bp,n+1 (−n)+ Bp,n+1 . =0 k n +2 Xk h i The summary by sections is as follows: Section 2 is the preliminary section where we give definitions and known results needed. In Section 3, we derive a recurrence relation for p-Bernoulli and a Raabe-type relation for geometric polynomials, which we need in the proofs of Theorem 6 and Theorem 8. In Section 4, we give the proofs of the results, mentioned above. 2 Preliminaries Geometric polynomials are defined by the exponential generating function [22] ∞ 1 tn = w (y) . (19) 1 − y (et − 1) n n! n=0 X They have an explicit formula n n + 1 w (y)= y (−1)n k k! (y + 1)k− , n> 0, (20) n k =1 Xk and a reflection formula y w (y) = (−1)n w (−y − 1) , for n> 0, (21) n y +1 n Moreover, these polynomials are related to p-Bernoulli numbers with an integral representation 0 p n+p+1 p +1 y w (y) dy = (−1) B −1 +1, for n> 1, p ≥ 0.