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A371743
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a(n) = Sum_{k=0..floor(n/2)} binomial(4*n-k,n-2*k).
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3
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1, 4, 29, 231, 1926, 16491, 143683, 1267395, 11282393, 101151544, 912011633, 8260998772, 75115815749, 685232639419, 6268299350776, 57478389714473, 528167137069958, 4862304525663579, 44836026545219765, 414048025058547788, 3828677665694353049
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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)^(3*n)).
a(n) ~ 2^(8*n + 5/2) / (11 * sqrt(Pi*n) * 3^(3*n - 1/2)). - Vaclav Kotesovec, Apr 05 2024
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PROG
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(PARI) a(n) = sum(k=0, n\2, binomial(4*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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