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A242982
Primes p such that p^2 divides 20^(p-1) - 1.
9
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
Amir Akbary and Sahar Siavashi, The Largest Known Wieferich Numbers, INTEGERS, 18(2018), A3. See Table 1 p. 5.
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, ", ")));
KEYWORD
nonn,hard,bref,more
AUTHOR
Felix Fröhlich, May 28 2014
STATUS
approved