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

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

Crossrefs

Cf. A000292.

Sequence in context: A029336 A211939 A010280 * A292148 A125266 A002016

Adjacent sequences: A318553 A318554 A318555 * A318557 A318558 A318559

Keyword

nonn

Author

Torlach Rush, Aug 28 2018

Status

approved