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 A123692 Primes p such that p^2 divides 5^(p-1) - 1. 25
 2, 20771, 40487, 53471161, 1645333507, 6692367337, 188748146801 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Dorais and Klyve proved that there are no further terms up to 9.7*10^14. a(6) and a(7) were found by Keller and Richstein (cf. Keller, Richstein, 2005). - Felix Fröhlich, Jan 06 2017 Prime terms of A242959. - Felix Fröhlich, Jan 06 2017 LINKS Amir Akbary and Sahar Siavashi, The Largest Known Wieferich Numbers, INTEGERS, 18(2018), A3. See Table 1 p. 5. Chris K. Caldwell, The Prime Glossary, Fermat quotient. François G. Dorais and Dominic Klyve, A Wieferich prime search up to p < 6.7*10^15, J. Integer Seq. 14 (2011), Art. 11.9.2, 1-14. W. Keller and J. Richstein, Solutions of the congruence a^p-1 == 1 (mod p^r), Math. Comp. 74 (2005), 927-936. A. Paszkiewicz, A new prime p for which the least primitive root (mod p) and the least primitive root (mod p^2) are not equal, Math. Comp. 78 (2009), 1193-1195. MATHEMATICA Select[Prime[Range[2500]], Divisible[5^(# - 1) - 1, #^2] &] (* Alonso del Arte, Aug 01 2014 *) PROG (PARI) N=10^9; default(primelimit, N); forprime(n=2, N, if(Mod(5, n^2)^(n-1)==1, print1(n, ", "))); \\ Joerg Arndt, May 01 2013 CROSSREFS Cf. A001220, A014127, A123693, A128667, A128668, A090968, A128669, A096082, A242959. Sequence in context: A173156 A214598 A242959 * A290741 A261362 A132942 Adjacent sequences:  A123689 A123690 A123691 * A123693 A123694 A123695 KEYWORD hard,nonn,more AUTHOR Max Alekseyev, Oct 07 2006 EXTENSIONS More terms from Alexander Adamchuk, Nov 27 2006 Updated by Max Alekseyev, Jan 29 2012 STATUS approved

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Last modified October 21 19:19 EDT 2019. Contains 328308 sequences. (Running on oeis4.)