OFFSET
0,2
PROG
(PARI) {a(n)=local(M=matrix(n+3, n+3, r, c, binomial(r*2^(c-2), c-1)), P); P=matrix(n+3, n+3, r, c, binomial((r+1)*2^(c-2), c-1)); (P~*M~^-1)[n+3, 3]/4^n}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Dec 31 2007
STATUS
approved