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A205789 Least positive integer k such that n divides k^4-j^4 for some j in [1,k-1]. 1
2, 3, 2, 3, 2, 4, 4, 3, 5, 3, 6, 4, 3, 8, 2, 3, 4, 9, 10, 3, 5, 12, 12, 4, 4, 5, 6, 8, 5, 4, 16, 5, 7, 5, 4, 9, 6, 20, 5, 3, 5, 10, 22, 12, 6, 24, 24, 4, 14, 7, 4, 5, 7, 9, 7, 8, 11, 7, 30, 4, 6, 32, 8, 6, 3, 14, 34, 5, 13, 8, 36, 9, 8, 7, 7, 20, 9, 5, 40, 3, 6, 9, 42, 10, 4, 44, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For a guide to related sequences, see A204892.

LINKS

Table of n, a(n) for n=1..87.

EXAMPLE

1 divides 2^4-1^4 -> k=2, j=1

2 divides 3^4-1^4 -> k=3, j=1

3 divides 2^4-1^4 -> k=2, j=1

4 divides 3^4-1^4 -> k=3, j=1

5 divides 2^4-1^4 -> k=2, j=1

6 divides 4^4-2^4 -> k=4, j=2

MATHEMATICA

s = Table[n^4, {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: A278354 A165005 A167530 * A029208 A322592 A329896

Adjacent sequences:  A205786 A205787 A205788 * A205790 A205791 A205792

KEYWORD

nonn

AUTHOR

Clark Kimberling, Feb 01 2012

STATUS

approved

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Last modified June 1 03:14 EDT 2020. Contains 334758 sequences. (Running on oeis4.)