OFFSET
0,2
COMMENTS
PROG
(PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+2, n+2, r, c, F=x; for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+2)))); polcoeff(F, c)); N=matrix(n+1, n+1, r, c, F=x; for(i=1, r, F=subst(F, x, x+x^2+x*O(x^(n+3)))); polcoeff(F, c)); P=matrix(n+1, n+1, r, c, M[r+1, c]); M=(P~*N~^-1); sum(k=1, n+1, M[n+1, k])}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 27 2009
STATUS
approved