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A123692
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Primes p such that p^2 divides 5^(p-1) - 1.
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31
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OFFSET
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1,1
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COMMENTS
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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
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LINKS
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MATHEMATICA
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Select[Prime[Range[2500]], Divisible[5^(# - 1) - 1, #^2] &] (* Alonso del Arte, Aug 01 2014 *)
Select[Prime[Range[55*10^6]], PowerMod[5, #-1, #^2]==1&] (* The program generates the first 4 terms of the sequence. *) (* Harvey P. Dale, Jan 29 2023 *)
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PROG
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(PARI)
N=10^9; default(primelimit, N);
forprime(n=2, N, if(Mod(5, n^2)^(n-1)==1, print1(n, ", ")));
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CROSSREFS
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KEYWORD
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hard,nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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