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A205563 Least positive integer k such that n divides 2k!-2j! for some j in [1,k-1]. 1
2, 2, 4, 3, 3, 4, 5, 3, 4, 3, 4, 4, 9, 5, 6, 5, 5, 4, 5, 6, 6, 4, 4, 5, 6, 9, 7, 6, 6, 6, 10, 5, 7, 5, 8, 4, 13, 5, 9, 6, 7, 6, 11, 4, 7, 4, 10, 5, 8, 6, 6, 9, 12, 7, 8, 8, 5, 6, 5, 6, 16, 10, 8, 5, 14, 7, 8, 6, 8, 8, 9, 7, 8, 13, 6, 5, 12, 9, 14, 6, 10, 7, 19, 6, 11, 11, 6, 7, 10, 7, 14 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For a guide to related sequences, see A204892.
LINKS
EXAMPLE
1 divides 2*2!-2*1! -> k=2, j=1
2 divides 2*2!-2*1! -> k=2, j=1
3 divides 2*4!-2*3! -> k=4, j=3
4 divides 2*3!-2*2! -> k=3, j=2
5 divides 2*3!-2*1! -> k=3, j=1
MATHEMATICA
s = Table[2n!, {n, 1, 120}];
lk = Table[
NestWhile[# + 1 &, 1,
Min[Table[Mod[s[[#]] - s[[j]], z], {j, 1, # - 1}]] =!= 0 &], {z, 1,
Length[s]}]
Table[NestWhile[# + 1 &, 1,
Mod[s[[lk[[j]]]] - s[[#]], j] =!= 0 &], {j, 1, Length[lk]}]
(* Peter J. C. Moses, Jan 27 2012 *)
CROSSREFS
Cf. A204892.
Sequence in context: A162439 A154417 A292421 * A147594 A305425 A212652
KEYWORD
nonn
AUTHOR
Clark Kimberling, Feb 01 2012
STATUS
approved

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Last modified May 23 07:28 EDT 2024. Contains 372760 sequences. (Running on oeis4.)