OFFSET
0,2
COMMENTS
PROG
(PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+3, n+3, r, c, F=x; for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+3)))); polcoeff(F, c)); N=matrix(n+2, n+2, r, c, M[r, c]); P=matrix(n+2, n+2, r, c, M[r+1, c]); (P~*N~^-1)[n+2, 2]}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 18 2007
STATUS
approved