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A371742
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a(n) = Sum_{k=0..floor(n/2)} binomial(3*n-k,n-2*k).
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4
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1, 3, 16, 92, 551, 3380, 21065, 132771, 843944, 5399802, 34731776, 224361283, 1454557294, 9458829681, 61670895633, 403003997300, 2638776935215, 17308508054848, 113709379928689, 748069400432262, 4927608724973776, 32495826854732633, 214521754579553129
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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/((1-x-x^2) * (1-x)^(2*n)).
a(n) ~ 3^(3*n + 3/2) / (5 * sqrt(Pi*n) * 2^(2*n)). - Vaclav Kotesovec, Apr 05 2024
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PROG
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(PARI) a(n) = sum(k=0, n\2, binomial(3*n-k, n-2*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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