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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

Table of n, a(n) for n=1..51.

Robert G. Wilson v, Table of n, a(n) for n = 1..10000 with -1 for large entries where a(n) has not yet been found

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

Cf. A128362, A128363, A128364, A128365, A128366, A128367, A128368, A128369, A129370, A128371, A128372.

Cf. A036236, A078457, A119678, A119679, A127816, A119715, A119714, A127817, A127818, A127819, A127820, A127821, A128154, A128155, A128156, A128157, A128158, A128159, A128160.

Cf. A128149, A128150, A128172.

Sequence in context: A221602 A092120 A059706 * A096481 A335363 A176618

Adjacent sequences:  A128358 A128359 A128360 * A128362 A128363 A128364

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 September 25 23:23 EDT 2020. Contains 337346 sequences. (Running on oeis4.)