A366590 G.f. A(x) satisfies A(x) = 1 + x^2*(1+x)^2*A(x)^3.
1, 0, 1, 2, 4, 12, 30, 84, 238, 680, 1993, 5882, 17575, 52976, 160870, 491924, 1512940, 4677672, 14529744, 45320640, 141897039, 445792908, 1404899598, 4440113940, 14069493813, 44689897200, 142268117566, 453839997836, 1450547245960, 4644492976232, 14896047099592
Offset: 0
Keywords
Programs
-
PARI
a(n) = sum(k=0, n\2, binomial(2*k, n-2*k)*binomial(3*k, k)/(2*k+1));
Formula
a(n) = Sum_{k=0..floor(n/2)} binomial(2*k,n-2*k) * binomial(3*k,k)/(2*k+1).