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 A128452 Least number k>n such that k^2 divides n^k - 1. 4
 4, 21, 6, 1555, 8, 889, 10, 111, 12, 253, 14, 2041, 16, 21, 18, 128583032925805678351, 20, 1432001198261, 22, 39, 24, 1081, 26, 55, 28, 171, 30, 279241, 32, 9641, 34, 1191, 36, 55, 38, 950123, 40, 1641, 42, 33661, 44, 32627169461820247, 46, 63, 48, 583223, 50 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 COMMENTS For prime p, p divides a(p+1). Quotients a(p+1)/p for prime p = A000040(n) are listed in A128456(n) which coincides with A128357(n) for n from 2 to 6. a(n) divides n^(n-1) - 1. LINKS FORMULA a(2n-1) = 2n. CROSSREFS Cf. A128456, A128357, A128356, A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128401, A128402, A128403, A128404. Sequence in context: A327085 A083192 A225540 * A202450 A144292 A329404 Adjacent sequences:  A128449 A128450 A128451 * A128453 A128454 A128455 KEYWORD nonn AUTHOR Alexander Adamchuk, Mar 05 2007. Mar 09 2007 EXTENSIONS More terms from Alexander Adamchuk, Mar 09 2007 Terms a(22) onward from Max Alekseyev, May 05 2010 STATUS approved

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Last modified February 24 10:37 EST 2020. Contains 332209 sequences. (Running on oeis4.)