A061213 a(n) = product of first n triangular numbers (A000217) + 1.

2, 4, 19, 181, 2701, 56701, 1587601, 57153601, 2571912001, 141455160001, 9336040560001, 728211163680001, 66267215894880001, 6958057668962400001, 834966920275488000001, 113555501157466368000001

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n=1,...,100

Formula

a(n) = {n(n+1)/2}*{a(n-1)-1}+1

Example

a(6) = 1 * 3 * 6 * 10 *15 * 21 + 1 = 56701

Maple

for n from 1 to 30 do printf(`%d, `, 1+product(j*(j+1)/2, j=1..n)) od:

Prog

(PARI) { for (n=1, 100, if (n>1, a=(n*(n + 1)/2)*(a - 1) + 1, a=2); write("b061213.txt", n, " ", a) ) } \\ Harry J. Smith, Jul 19 2009

Crossrefs

Equals A006472 + 1.

Sequence in context: A191563 A046082 A048774 * A063458 A332991 A132530

Adjacent sequences: A061210 A061211 A061212 * A061214 A061215 A061216

Keyword

nonn

Author

Amarnath Murthy, Apr 21 2001

Extensions

More terms from James A. Sellers, Apr 24 2001

OFFSET changed from 0,1 to 1,1 and EXAMPLE corrected by Harry J. Smith, Jul 19 2009

Status

approved