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A205561 Least positive integer k such that n divides (2k)!-(2j)! for some j in [1,k-1]. 1
2, 2, 3, 3, 4, 3, 5, 3, 4, 4, 2, 3, 8, 5, 4, 4, 10, 4, 4, 4, 5, 2, 4, 3, 4, 8, 6, 5, 3, 4, 5, 5, 4, 10, 5, 4, 20, 4, 8, 4, 11, 5, 10, 4, 4, 4, 5, 4, 6, 4, 10, 8, 6, 6, 4, 5, 8, 3, 13, 4, 8, 5, 5, 5, 8, 4, 16, 10, 4, 5, 7, 4, 4, 20, 4, 8, 7, 8, 11, 4, 6, 11, 22, 5, 10, 10, 3, 4, 5, 4, 8, 4 (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*3)!-(2*2)! -> k=3, j=2
4 divides (2*3)!-(2*2)! -> k=3, j=2
5 divides (2*4)!-(2*3)! -> k=4, j=3
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
Sequence in context: A110266 A349138 A309067 * A323636 A283367 A322528
KEYWORD
nonn
AUTHOR
Clark Kimberling, Feb 01 2012
STATUS
approved

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Last modified June 12 21:26 EDT 2024. Contains 373360 sequences. (Running on oeis4.)