A378461 a(n) = Sum_{k=0..n} binomial(n+k-1,k) * binomial(2*n+2*k-1,n-k).
1, 2, 16, 137, 1216, 11057, 102229, 956601, 9032680, 85893860, 821402341, 7891371303, 76105710253, 736364519399, 7144586617597, 69487754788517, 677259385478616, 6613163312601491, 64681617534027028, 633569272646345064, 6214190349161222941, 61023489213944162889
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+k-1, k)*binomial(2*n+2*k-1, n-k));
Formula
a(n) = [x^n] 1/(1 - x - x/(1 - x)^2)^n.