A371582 G.f. satisfies A(x) = ( 1 + x*A(x)^3 / (1 - x*A(x)) )^2.
1, 2, 15, 146, 1623, 19526, 247516, 3256118, 44037023, 608484766, 8552832116, 121908218724, 1757915510695, 25598937436696, 375916184707142, 5560517754432772, 82774606577536376, 1239110145377709862, 18641533742708676711, 281697878640036748684
Offset: 0
Keywords
Programs
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PARI
a(n, r=2, s=1, t=6, u=2) = 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
If g.f. satisfies A(x) = ( 1 + x*A(x)^(t/r) / (1 - x*A(x)^(u/r))^s )^r, then a(n) = 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).