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A123145
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a(1)=1, a(n) = a(n-1) if n == 1 (mod 4), otherwise a(n) = n * a(n-1) for n>=2.
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0
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1, 2, 6, 24, 24, 144, 1008, 8064, 8064, 80640, 887040, 10644480, 10644480, 149022720, 2235340800, 35765452800, 35765452800, 643778150400, 12231784857600, 244635697152000, 244635697152000, 5381985337344000, 123785662758912000, 2970855906213888000
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..24.
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FORMULA
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Conjecture: E.g.f.: E(x)=d(G(0))/dx where G(k) = 1 + x/(4*k+1 - x*(4*k+1)/(1 + x - x/(1 + x - x/(x + 1/G(k+1) )))), or shift on 1 left G(0) ; (continued fraction,5-step). - Sergei N. Gladkovskii, Nov 26 2012
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MATHEMATICA
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f[1]=1; f[n_] := f[n] = If[Mod[n, 4] - 1 == 0, f[n - 1], n*f[n - 1]] a = Table[f[n], {n, 1, 20}]
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CROSSREFS
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Cf. A007559, A007696.
Sequence in context: A060068 A099732 A118381 * A079433 A110728 A190424
Adjacent sequences: A123142 A123143 A123144 * A123146 A123147 A123148
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KEYWORD
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nonn
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AUTHOR
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Roger Bagula, Oct 01 2006
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EXTENSIONS
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Edited by N. J. A. Sloane, Oct 04 2006
More terms by Bruno Berselli, Nov 27 2012
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STATUS
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approved
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