A371680 G.f. satisfies A(x) = ( 1 + x * A(x)^2 * (1 + A(x)) )^2.
1, 4, 44, 648, 10960, 200992, 3886928, 78043488, 1611405504, 33998715264, 729793915264, 15886841223936, 349900041893376, 7782694227059712, 174573007616191744, 3944500600180286976, 89696369377912622080, 2051147782339517224960
Offset: 0
Keywords
Programs
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PARI
a(n, r=2, t=4, u=2) = r*sum(k=0, n, binomial(n, k)*binomial(t*n+u*k+r, n)/(t*n+u*k+r));
Formula
G.f.: B(x)^2 where B(x) is the g.f. of A363380.
a(n) = Sum_{k=0..n} binomial(n,k) * binomial(4*n+2*k+2,n)/(2*n+k+1).