A371614 G.f. satisfies A(x) = ( 1 + x / (1 - x*A(x)^2)^2 )^2.
1, 2, 5, 26, 138, 814, 5051, 32550, 215792, 1461934, 10077345, 70450980, 498328320, 3559894566, 25646621725, 186122575840, 1359384244220, 9984580141702, 73703387448245, 546492958156148, 4068417329371228, 30397841636794944, 227872480308702892
Offset: 0
Keywords
Programs
-
PARI
a(n, r=2, s=2, t=0, u=4) = r*sum(k=0, n, binomial(t*k+u*(n-k)+r, k)*binomial(n+(s-1)*k-1, n-k)/(t*k+u*(n-k)+r));
Formula
a(n) = Sum_{k=0..n} binomial(4*(n-k)+2,k) * binomial(n+k-1,n-k)/(2*(n-k)+1).