A379189 G.f. A(x) satisfies A(x) = 1/((1 - x*A(x)^3) * (1 - x*A(x))).
1, 2, 11, 84, 749, 7297, 75263, 807795, 8928259, 100930845, 1161556834, 13563086118, 160286280443, 1913502807883, 23041637546674, 279535792627983, 3413404764685607, 41920395344282046, 517450364496878615, 6416254102356745484, 79884728250064030602, 998261210034672052421
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, binomial(n+3*k+1, k)*binomial(2*n+k, n-k)/(n+3*k+1));
Formula
a(n) = Sum_{k=0..n} binomial(n+3*k+1,k) * binomial(2*n+k,n-k)/(n+3*k+1).