A379249 G.f. A(x) satisfies A(x) = (1 + x*A(x)^3) * (1 + x*A(x))^2.
1, 3, 18, 148, 1403, 14417, 156161, 1755664, 20293341, 239654554, 2879027132, 35072400492, 432238230583, 5379422216020, 67513288465855, 853481985400772, 10858099927189575, 138912471444569435, 1786014309638224994, 23065160118446902506, 299062458173041384523
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+2*k+1, k)*binomial(2*n+4*k+2, n-k)/(n+2*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(n+2*k+1,k) * binomial(2*n+4*k+2,n-k)/(n+2*k+1).