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A368966
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Expansion of (1/x) * Series_Reversion( x * (1-x) * (1-x-x^3)^2 ).
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8
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1, 3, 15, 93, 644, 4769, 36953, 295867, 2428373, 20322566, 172759032, 1487632887, 12948891408, 113748663495, 1007117650350, 8978151790011, 80519598139947, 725976573163011, 6576546244337046, 59829384514916820, 546375444906314661, 5006934930385254672
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(2*n+k+1,k) * binomial(4*n-2*k+2,n-3*k).
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PROG
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(PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x)*(1-x-x^3)^2)/x)
(PARI) a(n, s=3, t=2, u=1) = sum(k=0, n\s, binomial(t*(n+1)+k-1, k)*binomial((t+u+1)*(n+1)-(s-1)*k-2, n-s*k))/(n+1);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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