A318556 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

A318556

a(n) is the number of lesser tetrahedral numbers that divide the n-th tetrahedral number.

0, 1, 1, 3, 1, 2, 2, 4, 1, 4, 1, 2, 2, 6, 4, 2, 1, 4, 3, 6, 1, 2, 4, 4, 1, 4, 1, 5, 1, 4, 2, 2, 2, 6, 3, 2, 1, 4, 4, 6, 1, 2, 3, 6, 1, 2, 3, 7, 2, 4, 1, 2, 2, 11, 8, 3, 1, 4, 2, 4, 1, 4, 11, 6, 1, 2, 1, 5, 2, 8, 2, 2, 1, 4, 4, 4, 1, 4, 5, 5, 1, 2, 3, 5, 1, 2, 2, 7, 3, 8, 1, 2, 1, 4, 4, 3, 1, 9

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,4

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = Sum_{m=1..n-1} [0 = A000292(n) mod A000292(m)]. Here [] is the Iverson bracket function.

EXAMPLE

t(4) is 20 and 20 is divisible by t(1)=1, t(2)=4 and t(3)=10, so a(4)=3.

PROG

(PARI) t(n) = n*(n+1)*(n+2)/6;

a(n) = my(tn=n*(n+1)*(n+2)/6); sum(k=1, n-1, (tn % t(k)) == 0); \\ Michel Marcus, Sep 27 2018