OFFSET
1,2
PROG
(PARI) {a(n)=local(G=serreverse(x-x^2+O(x^(n+2)))); for(i=2, n, G=subst(G, x, G)); polcoeff(G, n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Mar 28 2009
STATUS
approved