A371580 G.f. satisfies A(x) = ( 1 + x*A(x)^(5/2) * (1 + x)^2 )^2.
1, 2, 15, 126, 1211, 12544, 136668, 1543696, 17914325, 212308682, 2558783193, 31265632206, 386430721728, 4822586987324, 60686262591525, 769167948066520, 9810280980482827, 125819903217235130, 1621648696092783746, 20993171222948561746, 272848383910348808089
Offset: 0
Keywords
Programs
-
PARI
a(n, r=2, s=2, t=5, u=0) = r*sum(k=0, n, binomial(t*k+u*(n-k)+r, k)*binomial(s*k, n-k)/(t*k+u*(n-k)+r));
Formula
a(n) = 2 * Sum_{k=0..n} binomial(5*k+2,k) * binomial(2*k,n-k)/(5*k+2).