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A243107
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Number of terms in a bordered skew determinant.
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2
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1, 1, 2, 4, 13, 41, 226, 1072, 9059, 58123, 657766, 5268836, 73980787, 707506879, 11823958238, 131277234376, 2542107619081, 32122718085497, 706963537444114, 10015472595953908, 246853433179370621, 3874536631479770761, 105709617658879558402
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OFFSET
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0,3
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COMMENTS
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Possibly a different attempt to count the same bordered skew determinants as in A002772.
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LINKS
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FORMULA
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a(n) = Sum_{k=0..floor(n/2)} binomial(n, n - 2*k) * A002370(k).
E.g.f.: exp(x+x^2/4) / (1-x^2)^(1/4).
a(n) ~ n! * GAMMA(3/4) * (exp(5/4) + (-1)^n * exp(-3/4)) / (Pi * 2^(3/4)* n^(3/4)). - Vaclav Kotesovec, Aug 20 2014
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MAPLE
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a:= proc(n) option remember; `if`(n<4, [1$2, 2, 4][n+1],
(2*a(n-1)+2*(n-1)^2*a(n-2)-2*(n-1)*(n-2)*a(n-3)
-(n-1)*(n-2)*(n-3)*a(n-4))/2)
end:
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MATHEMATICA
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b[n_] := Gamma[n+1/2] HypergeometricPFQ[{1/4, -n}, {}, -4]/Sqrt[Pi];
a[n_] := Sum[Binomial[n, n-2k] b[k], {k, 0, n/2}];
a /@ Range[0, 30]
(* Second program: *)
a[n_] := a[n] = If[n < 4, {1, 1, 2, 4}[[n+1]], (2a[n-1] + 2(n-1)^2 a[n-2] - 2(n-1)(n-2)a[n-3] - (n-1)(n-2)(n-3) a[n-4])/2];
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PROG
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(PARI) my(x='x+O('x^66)); Vec(serlaplace(exp(x+x^2/4) / (1-x^2)^(1/4))) \\ Joerg Arndt, Aug 20 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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