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Primes p such that p^2 divides 13^(p-1) - 1.
21

%I #16 Apr 03 2023 10:36:11

%S 2,863,1747591

%N Primes p such that p^2 divides 13^(p-1) - 1.

%C No further terms up to 3.127*10^13.

%H Amir Akbary and Sahar Siavashi, <a href="http://math.colgate.edu/~integers/s3/s3.Abstract.html">The Largest Known Wieferich Numbers</a>, INTEGERS, 18(2018), A3. See Table 1 p. 5.

%H C. K. Caldwell, <a href="https://t5k.org/glossary/xpage/FermatQuotient.html">Fermat quotient</a>

%H Richard Fischer, <a href="http://www.fermatquotient.com/FermatQuotienten/">Fermat quotients B^(P-1) == 1 (mod P^2)</a>

%t Select[Prime[Range[5*10^7]], Mod[ 13^(# - 1) - 1, #^2] == 0 &] (* _G. C. Greubel_, Jan 18 2018 *)

%Y Cf. A001220, A014127, A123692, A123693, A128668, A090968, A128669, A039951

%K bref,hard,more,nonn

%O 1,1

%A _Alexander Adamchuk_, Mar 26 2007