A261401 Expansion of 1 + Sum_{n>=1} ( q^(n^2)/Product_{i=1..n} ((1+q^(2*i))^2) ).

1, 1, 0, -2, 1, 3, -2, -4, 1, 6, 0, -8, 2, 8, -4, -10, 3, 15, -2, -16, 4, 16, -8, -22, 7, 28, -2, -30, 7, 33, -14, -40, 9, 48, -8, -54, 16, 60, -20, -68, 19, 82, -16, -94, 21, 98, -34, -116, 32, 138, -24, -146, 40, 165, -54, -190, 45, 212, -46, -240

Offset: 0

Author

N. J. A. Sloane, Aug 20 2015

Keywords

• sign

Crossrefs

Suggested by the g.f.'s for A000025 and A053250.

Programs

Maple

phi:=1+add( q^(n^2)/mul((1+q^(2*i))^2,i=1..n), n=1..61):
series(phi,q,60);
seriestolist(%);