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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

Table of n, a(n) for n=3..49.

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.)