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A127105 Numbers n such that n^2 divides 5^n-1. 28
1, 2, 4, 6, 12, 42, 52, 84, 156, 186, 372, 1092, 1218, 1302, 1806, 2436, 2604, 2756, 3612, 4836, 5334, 7212, 8268, 10668, 12324, 15918, 18858, 24492, 31668, 31836, 33852, 37716, 37758, 46956, 50484, 52374, 55986, 57876, 71862, 75516, 86268 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Subset of A067946 (numbers n such that n divides 5^n-1).

LINKS

Robert Israel, Table of n, a(n) for n = 1..1000

Taro Morishima, Über die Fermatsche Vermutung, Proc. Imp. Acad., Volume 4, Number 10 (1928), 590-592.

MAPLE

select(t -> (5 &^t - 1) mod (t^2) = 0, [$1..10^5]); # Robert Israel, Jul 15 2018

MATHEMATICA

Select[Range[30000], IntegerQ[(PowerMod[5, #, #^2 ]-1)/#^2 ]&]

PROG

(PARI) isok(n) = Mod(5, n^2)^n == 1; \\ Michel Marcus, Apr 23 2017

CROSSREFS

Cf. A127100, A127101, A127102, A127103, A123104, A127106, A127107, A127092.

Cf. A067946 (numbers n such that n divides 5^n-1).

Sequence in context: A180213 A081457 A261206 * A196444 A307617 A325278

Adjacent sequences:  A127102 A127103 A127104 * A127106 A127107 A127108

KEYWORD

nonn

AUTHOR

Alexander Adamchuk, Jan 05 2007

EXTENSIONS

More terms from Ryan Propper and Alexander Adamchuk, Jan 05 2007

STATUS

approved

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Last modified September 28 12:34 EDT 2020. Contains 337393 sequences. (Running on oeis4.)