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A128361 a(n) = least k such that the remainder when 21^k is divided by k is n. 17
2, 19, 6, 17, 218, 15, 14, 13, 12, 11, 86, 9249, 214, 133, 69, 4084085, 106, 39, 422, 581831, 23, 5053, 38, 9237, 26, 775, 46, 1253, 206, 51, 82, 671, 34, 617741981, 58, 45, 202, 289, 87, 6401, 185, 217, 341, 3485351, 66, 2718013, 394, 111, 56, 8064317, 75 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
t = Table[0, {10000}]; k = 1; While[k < 3000000000, a = PowerMod[21, k, k]; If[a < 10001 && t[[a]] == 0, t[[a]] = k]; k++ ]; t (* Robert G. Wilson v, Jun 25 2009 *)
lk[n_]:=Module[{k=1}, While[PowerMod[21, k, k]!=n, k++]; k]; Array[lk, 60] (* The program takes a long time to run *) (* Harvey P. Dale, Oct 22 2016 *)
CROSSREFS
Sequence in context: A358980 A092120 A059706 * A096481 A335363 A176618
KEYWORD
hard,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
a(16) - a(51) from Robert G. Wilson v, Jun 25 2009
STATUS
approved

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Last modified March 19 04:58 EDT 2024. Contains 370952 sequences. (Running on oeis4.)