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 A123145 a(1)=1, a(n) = a(n-1) if n == 1 (mod 4), otherwise a(n) = n * a(n-1) for n>=2. 0
 1, 2, 6, 24, 24, 144, 1008, 8064, 8064, 80640, 887040, 10644480, 10644480, 149022720, 2235340800, 35765452800, 35765452800, 643778150400, 12231784857600, 244635697152000, 244635697152000, 5381985337344000, 123785662758912000, 2970855906213888000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA 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 MATHEMATICA 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}] CROSSREFS Cf. A007559, A007696. Sequence in context: A060068 A099732 A118381 * A079433 A110728 A190424 Adjacent sequences:  A123142 A123143 A123144 * A123146 A123147 A123148 KEYWORD nonn AUTHOR Roger Bagula, Oct 01 2006 EXTENSIONS Edited by N. J. A. Sloane, Oct 04 2006 More terms by Bruno Berselli, Nov 27 2012 STATUS approved

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