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A123144 a(n) = if mod[n, 3] - 1 == 0 then a(n - 1) else n*a(n - 1). 1
1, 2, 6, 6, 30, 180, 180, 1440, 12960, 12960, 142560, 1710720, 1710720, 23950080, 359251200, 359251200, 6107270400, 109930867200, 109930867200, 2198617344000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Without duplicates this sequence is {1, 2, 8, 48, 384, 3840, 46080, 645120, ...}

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..632

MATHEMATICA

f[1]=1; f[n_] := f[n] = If[Mod[n, 3] - 1 == 0, f[n - 1], n*f[n - 1]] a = Table[f[n], {n, 1, 20}]

nxt[{n_, a_}]:={n+1, If[Mod[n+1, 3]==1, a, a(n+1)]}; Transpose[NestList[nxt, {1, 1}, 20]][[2]] (* Harvey P. Dale, Jul 22 2014 *)

CROSSREFS

Cf. A007559.

Sequence in context: A093364 A113461 A061558 * A179215 A069260 A056603

Adjacent sequences:  A123141 A123142 A123143 * A123145 A123146 A123147

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Oct 01 2006

EXTENSIONS

Edited by N. J. A. Sloane, Oct 04 2006

STATUS

approved

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Last modified January 18 04:47 EST 2019. Contains 319269 sequences. (Running on oeis4.)