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A370098
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a(n) = Sum_{k=0..n} binomial(3*n,k) * binomial(4*n-k-1,n-k).
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4
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1, 6, 72, 978, 14016, 207006, 3116952, 47568618, 733189632, 11387193846, 177923724072, 2793666465090, 44042615547456, 696708049377294, 11053262513080440, 175800225426741978, 2802193910116429824, 44752001810800994022, 715924864099841086728
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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) = [x^n] ( (1+x)^3/(1-x)^3 )^n.
The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x*(1-x)^3/(1+x)^3 ). See A365843.
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PROG
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(PARI) a(n) = sum(k=0, n, binomial(3*n, k)*binomial(4*n-k-1, n-k));
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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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