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A307158
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a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n,3*k)^2.
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2
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1, 1, 1, 0, -15, -99, -398, -1175, -2351, 0, 29601, 183195, 756978, 2351805, 4885791, 0, -63746991, -400000275, -1675991918, -5274560891, -11081420615, 0, 147257373891, 931226954949, 3929550225586, 12446852889901, 26304183607651, 0, -353181028924809
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OFFSET
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0,5
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LINKS
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FORMULA
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a(6*n+3) = 0 for n >= 0.
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MATHEMATICA
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a[n_] := Sum[(-1)^k * Binomial[n, 3*k]^2, {k, 0, Floor[n/3]}]; Array[a, 30, 0] (* Amiram Eldar, May 20 2021 *)
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PROG
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(PARI) {a(n) = sum(k=0, n\3, (-1)^k*binomial(n, 3*k)^2)}
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CROSSREFS
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Central coefficients of number triangle A307156.
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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