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 A081763 Primes p such that p*(p-1) divides 3^(p-1)-1. 1
 2, 5, 17, 41, 101, 257, 401, 641, 881, 1361, 1601, 2441, 3089, 4001, 5441, 5501, 6101, 12101, 13121, 13421, 14081, 14741, 15101, 16001, 18041, 20201, 25301, 25601, 29921, 30881, 32801, 35201, 39041, 39161, 40961, 49409, 53681, 54401, 54449 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms == 2 (mod 3).  Also most are congruent to 1 (mod 10). Those that are not: 2, 5, 17, 257, 3089, 49409, 54449, 65537, 83969, 149057, .... - Robert G. Wilson v, Dec 02 2013 Number of terms < 10^k: 2, 4, 9, 17, 49, 105, 244, 574, 1388, .... - Robert G. Wilson v, Dec 02 2013 LINKS Robert G. Wilson v, Table of n, a(n) for n = 1..1637 MATHEMATICA Select[ Prime@ Range@ 6000, PowerMod[3, # - 1, # (# - 1)] == 1 &] (* Robert G. Wilson v, Dec 02 2013 *) PROG (PARI) lista(nn) = forprime(p=2, nn, if (! ((3^(p-1)-1) % (p*(p-1))), print1(p, ", "))) \\ Michel Marcus, Dec 02 2013 (PARI) is(n)=isprime(n) && Mod(3, n^2-n)^(n-1)==1 \\ Charles R Greathouse IV, Dec 02 2013 CROSSREFS Sequence in context: A118500 A323427 A080898 * A013918 A007351 A300692 Adjacent sequences:  A081760 A081761 A081762 * A081764 A081765 A081766 KEYWORD nonn AUTHOR Benoit Cloitre, Apr 09 2003 EXTENSIONS Missing term 2 added to sequence by Robert G. Wilson v, Dec 02 2013 STATUS approved

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Last modified September 20 10:10 EDT 2019. Contains 327229 sequences. (Running on oeis4.)