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A008336
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a(n+1) = a(n)/n if n|a(n) else a(n)*n, a(1) = 1.
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15
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1, 1, 2, 6, 24, 120, 20, 140, 1120, 10080, 1008, 11088, 924, 12012, 858, 12870, 205920, 3500640, 194480, 3695120, 184756, 3879876, 176358, 4056234, 97349616, 2433740400, 93605400, 2527345800
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OFFSET
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1,3
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COMMENTS
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The graph of log_10(a(n)+1) seems to suggest that log(a(n)) is asymptotic to C*n where C is approximately 0.8. - Daniel Forgues, Sep 18 2011
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LINKS
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Indranil Ghosh, Table of n, a(n) for n = 1..2732 (terms 1..1000 from T. D. Noe)
R. K. Guy and R. Nowakowski, Unsolved Problems, Amer. Math. Monthly, vol. 102 (1995), circa page 924.
Nick Hobson, Python program for this sequence
N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).
Index entries for sequences related to Recamán's sequence
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MAPLE
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A008336 := proc(n) option remember; if n = 1 then 1 elif A008336(n-1) mod (n-1) = 0 then A008336(n-1)/(n-1) else A008336(n-1)*(n-1); fi; end;
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MATHEMATICA
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a[n_] := a[n] = If[ Divisible[ a[n-1], n-1], a[n-1]/(n-1), a[n-1]*(n-1)]; a[1] = 1; Table[a[n], {n, 1, 28}] (* Jean-François Alcover, Dec 02 2011 *)
nxt[{n_, a_}]:={n+1, If[Divisible[a, n], a/n, n*a]}; Transpose[ NestList[ nxt, {1, 1}, 30]][[2]] (* Harvey P. Dale, May 09 2016 *)
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PROG
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(Haskell)
a008336 n = a008336_list !! (n-1)
a008336_list = 1 : zipWith (/*) a008336_list [1..] where
x /* y = if x `mod` y == 0 then x `div` y else x*y
-- Reinhard Zumkeller, Feb 22 2012, Oct 25 2010
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CROSSREFS
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Cf. A005132, A065422.
Cf. A195504 Product of numbers up to n-1 used as divisors in A008336(n), n >= 2; a(1) = 1.
Sequence in context: A360300 A065422 A260850 * A360298 A033643 A050211
Adjacent sequences: A008333 A008334 A008335 * A008337 A008338 A008339
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KEYWORD
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nonn,easy,nice,look
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AUTHOR
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Bernardo Recamán
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STATUS
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approved
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