OFFSET
1,4
PROG
(PARI) {a(n)=local(A); if(n<1, 0, A=x+x*O(x^n); for(k=0, n-2, A+=A^2*x^k); polcoeff(A, n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Nov 04 2006
STATUS
approved