A366273 G.f. A(x) satisfies A(x) = 1 + x*(1 + x)^4*A(x)^5.
1, 1, 9, 81, 849, 9681, 116601, 1459809, 18809121, 247782369, 3322209001, 45187029809, 621970864241, 8647376531249, 121261376439641, 1713085987837889, 24358211622230081, 348325689458584769, 5006342381846708681, 72279683684984063249, 1047789195353379807121
Offset: 0
Keywords
Programs
-
PARI
a(n) = sum(k=0, n, binomial(4*k, n-k)*binomial(5*k, k)/(4*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(4*k,n-k) * binomial(5*k,k)/(4*k+1).