OFFSET
1,3
COMMENTS
Euler transform of period 3 sequence [1,1,-4,...].
a(25n-10)=5a(n). a(5n)=0 unless n == 3 (mod 5).
FORMULA
G.f.: x Product_{k>0} (1-x^(3k))^5/(1-x^k).
PROG
(PARI) a(n)=local(X); if(n<1, 0, X=x+x*O(x^n); n--; polcoeff(eta(X^3)^5/eta(X), n))
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Apr 18 2004
STATUS
approved