A261633 Expansion of Product_{k>=0} (1+x^(3*k+1))^3.

1, 3, 3, 1, 3, 9, 9, 6, 12, 18, 15, 21, 37, 36, 33, 55, 69, 66, 90, 117, 111, 136, 195, 204, 217, 294, 330, 342, 447, 531, 541, 657, 804, 839, 978, 1215, 1288, 1419, 1755, 1936, 2094, 2535, 2846, 3027, 3588, 4123, 4392, 5073, 5869, 6261, 7080

Offset

0,2

Links

Table of n, a(n) for n=0..50.

Formula

a(n) ~ exp(Pi*sqrt(n/3)) / (2 * 3^(1/4) * n^(3/4)).

Mathematica

nmax=50; CoefficientList[Series[Product[(1+x^(3*k+1))^3, {k, 0, nmax}], {x, 0, nmax}], x]

Crossrefs

Cf. A261612, A261615, A261634.

Sequence in context: A262220 A325254 A202252 * A277103 A120919 A032240

Adjacent sequences: A261630 A261631 A261632 * A261634 A261635 A261636

Keyword

nonn

Author

Vaclav Kotesovec, Aug 27 2015

Status

approved