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A124995
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a(n) is the constant term in expansion of Product_{ k = 1..n } (x^k + 1/x^k)^3.
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4
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1, 0, 0, 62, 332, 0, 0, 80006, 531524, 0, 0, 173607568, 1226700784, 0, 0, 455805857978, 3321800235936, 0, 0, 1325490660318216, 9841000101286172, 0, 0, 4108826483323392880, 30886378286619335592, 0, 0, 13306426381421174346512, 100916492010297213463566
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OFFSET
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0,4
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COMMENTS
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a(n) is the coefficient of x^(3*n*(n+1)/2) in Product_{k=0..n} (x^(2*k)+1)^3.
a(n) = 0 if n == 1 or 2 (mod 4). (End)
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LINKS
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MAPLE
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seq(coeff(mul(x^k+1/x^k, k=1..n)^3, x, 0), n=0..50); # Robert Israel, Nov 09 2017
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PROG
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(PARI) a(n) = polcoef(prod(k=1, n, (x^k + 1/x^k)^3), 0); \\ Michel Marcus, Jan 07 2021
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CROSSREFS
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For constant term in expansion of Product_{ k = 1..n } (x^k + 1/x^k)^q for other values of q see A063865, A047653, A124996.
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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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