OFFSET
0,2
FORMULA
a(n) = [x^(n*(n+1)/2)] [Sum_{k>=0} x^(k*(k+1)/2)]^4/(1-x).
PROG
(PARI) {a(n)=local(X=x+x*O(x^(n*(n+1)/2))); polcoeff((eta(X^2)^2/eta(X))^4/(1-X), n*(n+1)/2)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jun 27 2005
STATUS
approved