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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: A358980 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 27 01:21 EDT 2023. Contains 365669 sequences. (Running on oeis4.)