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A128357 Quotients A128356(n)/Prime[n]. 8
10, 7, 311, 127, 23, 157, 343927, 7805561, 47, 9629, 311, 25679, 821, 1470086279, 12409, 71233, 1232333, 2443783, 2939291, 71711, 352883, 181113265579, 167, 105199, 3881, 1314520253, 619, 20759, 117503, 1162660843, 1880415721, 263 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A128356(n) = {20, 21, 1555, 889, 253, 2041, 5846759, ...} = Least number k>1 (that is not the power of prime p) such that k divides (p+1)^k-1, where p = Prime[n]. Most listed terms are primes, except a(7) = 20231*17 and a(8) = 410819*19. a(15) = 12409. a(16) = 71233.

Note that all prime listed terms of a(n) coincide with terms of A128456(n) = {2,7,311,127,23,157,7563707819165039903,75368484119,47,9629,311,25679,821,...} = least prime factor of ((p+1)^p - 1)/p^2, where p = Prime[n].

LINKS

Table of n, a(n) for n=1..32.

CROSSREFS

Cf. A128356 = Least number k>1 (that is not the power of prime p) such that k divides (p+1)^k-1, where p = Prime[n]. Cf. A014960, A128360, A128358, A014960, A014956, A014951, A014949, A014946, A014945, A067945.

Cf. A128456 = least prime factor of ((p+1)^p - 1)/p^2, where p = Prime[n].

Sequence in context: A227473 A038309 A185264 * A024134 A180197 A280871

Adjacent sequences:  A128354 A128355 A128356 * A128358 A128359 A128360

KEYWORD

hard,nonn

AUTHOR

Alexander Adamchuk, Mar 02 2007, Mar 09 2007

EXTENSIONS

Terms a(14) onwards from Max Alekseyev, Feb 08 2010

STATUS

approved

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Last modified February 23 23:03 EST 2018. Contains 299595 sequences. (Running on oeis4.)