A242982 Primes p such that p^2 divides 20^(p-1) - 1.

281, 46457, 9377747, 122959073

Offset

1,1

Comments

Base 20 Wieferich primes. According to Richard Fischer, there is no other term up to approximately 5*10^13.

Links

Table of n, a(n) for n=1..4.

Amir Akbary and Sahar Siavashi, The Largest Known Wieferich Numbers, INTEGERS, 18(2018), A3. See Table 1 p. 5.

R. Fischer, Thema: Fermatquotient B^(P-1) == 1 (mod P^2)

Mathematica

Select[Prime[Range[1000000]], PowerMod[20, # - 1, #^2] == 1 &] (* Robert Price, May 17 2019 *)

Prog

(PARI) forprime(n=2, 10^9, if(Mod(20, n^2)^(n-1)==1, print1(n, ", ")));

Crossrefs

Cf. A001220, A014127, A123692, A212583, A123693, A045616, A111027, A039951, A096082.

Sequence in context: A289543 A270964 A185710 * A255387 A320706 A356854

Adjacent sequences: A242979 A242980 A242981 * A242983 A242984 A242985

Keyword

nonn,hard,bref,more

Author

Felix Fröhlich, May 28 2014

Status

approved