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A370102
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a(n) = Sum_{k=0..n} binomial(4*n,k) * binomial(5*n-k-1,n-k).
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4
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1, 8, 128, 2312, 44032, 864008, 17282432, 350353928, 7172939776, 147972367880, 3070951360128, 64044689834760, 1341056098444288, 28176478479561992, 593725756425591680, 12542160174109922312, 265525958014053580800, 5632170795392966388744
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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)^4/(1-x)^4 )^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)^4/(1+x)^4 ). See A365847.
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PROG
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(PARI) a(n) = sum(k=0, n, binomial(4*n, k)*binomial(5*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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