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

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

Offset: 1

Author

Amarnath Murthy, Apr 21 2001

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Cf. A000217, A006472.

Programs

Maple

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

PARI

a(n) = { 1 + prod(k=1, n, k*(k + 1)/2) } \\ Harry J. Smith, Jul 19 2009

Formula

a(n) = A006472(n+1) + 1.

a(n) = (n*(n+1)/2)*(a(n-1)-1) + 1.

Extensions

More terms from James Sellers, Apr 24 2001

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