New results on the least common multiple of consecutive integers Bakir FARHI and Daniel KANE Département de Mathématiques, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France.
[email protected] Harvard University, Department of Mathematics 1 Oxford Street, Cambridge MA 02139, USA.
[email protected] Abstract When studying the least common multiple of some nite sequences of integers, the rst author introduced the interesting arithmetic functions , dened by n(n+1):::(n+k) . He gk (k 2 N) gk(n) := lcm(n;n+1;:::;n+k) (8n 2 N n f0g) proved that is periodic and is a period of . He raised gk (k 2 N) k! gk the open problem consisting to determine the smallest positive period Pk of gk. Very recently, S. Hong and Y. Yang have improved the period k! of gk to lcm(1; 2; : : : ; k). In addition, they have conjectured that Pk is always a multiple of the positive integer lcm(1;2;:::;k;k+1) . An immediate k+1 consequence of this conjecture states that if (k+1) is prime then the exact period of gk is precisely equal to lcm(1; 2; : : : ; k). In this paper, we rst prove the conjecture of S. Hong and Y. Yang and then we give the exact value of . We deduce, as a corollary, Pk (k 2 N) that Pk is equal to the part of lcm(1; 2; : : : ; k) not divisible by some prime. MSC: 11A05 Keywords: Least common multiple; arithmetic function; exact period. 1 Introduction Throughout this paper, we let N∗ denote the set N n f0g of positive integers.