OFFSET
1,1
FORMULA
a(q) = Prod_{k>0} (1 - q^k)^-a(k).
PROG
(PARI) {a(n) = local(A, S); if( n<1, 0, A = 1 + x * O(x^n); S = sum( k= 1, n, 6 * sumdiv( k, d, kronecker( d, 3)) * x^k, A); for( k = 1, n-1, S *= (A - x^k) ^ polcoeff( S, k)); polcoeff( S, n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Jul 08 2011
STATUS
approved