A125775 Numbers k such that 5^k mod k = 5^k mod k^2.

1, 2, 4, 5, 6, 12, 25, 42, 52, 84, 125, 156, 186, 372, 625, 1092, 1218, 1302, 1806, 2436, 2604, 2756, 3125, 3612, 4836, 5334, 7212, 8268, 10668, 12324, 15625, 15918, 18858, 19140, 20771, 24492, 26080, 31668, 31836, 33852, 37716, 37758, 40487, 41542

Offset

1,2

Comments

Includes all powers of 5 (A000351).

a(2) = 2, a(4) = 5, a(35) = 20771 and a(43) = 40487 are the only listed primes. More known primes are listed in A123692.

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Mathematica

Do[f=PowerMod[5, n, n]; g=PowerMod[5, n, n^2]; If[f==g, Print[n]], {n, 1, 1000000}]
Select[Range[42000], PowerMod[5, #, #]==PowerMod[5, #, #^2]&] (* Harvey P. Dale, Aug 20 2022 *)

Crossrefs

Cf. A000351, A123692, A068535, A125773, A125774.

Sequence in context: A182109 A006539 A031150 * A331624 A191165 A360994

Adjacent sequences: A125772 A125773 A125774 * A125776 A125777 A125778

Keyword

nonn

Author

Alexander Adamchuk, Dec 07 2006

Status

approved