A366698 G.f. satisfies A(x) = (1 + x)^2 + x*A(x)^4.
1, 3, 13, 106, 1000, 10315, 112732, 1282262, 15021212, 179994093, 2195807684, 27179964798, 340514877488, 4309512389582, 55014793453124, 707582318505678, 9160219144520568, 119268621622902920, 1560830776582842660, 20519083242145870778, 270851956372499374728
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(2*(3*k+1), n-k)*binomial(4*k, k)/(3*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(2*(3*k+1),n-k) * binomial(4*k,k)/(3*k+1).