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A369231
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Expansion of (1/x) * Series_Reversion( x * (1-x)^3 / (1-x+x^3)^2 ).
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3
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1, 1, 2, 7, 26, 98, 385, 1569, 6556, 27908, 120624, 528030, 2336202, 10430155, 46930285, 212597901, 968833424, 4438398734, 20428750419, 94424634294, 438104297376, 2039690282940, 9526029685218, 44617396906698, 209526541600978, 986339358246758, 4653571637230839
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OFFSET
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0,3
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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+2,k) * binomial(2*n-2*k,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)^3/(1-x+x^3)^2)/x)
(PARI) a(n, s=3, t=2, u=3) = sum(k=0, n\s, binomial(t*(n+1), k)*binomial((u-t+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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