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A081763 Primes p such that p*(p-1) divides 3^(p-1)-1. 1

%I

%S 2,5,17,41,101,257,401,641,881,1361,1601,2441,3089,4001,5441,5501,

%T 6101,12101,13121,13421,14081,14741,15101,16001,18041,20201,25301,

%U 25601,29921,30881,32801,35201,39041,39161,40961,49409,53681,54401,54449

%N Primes p such that p*(p-1) divides 3^(p-1)-1.

%C 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

%C Number of terms < 10^k: 2, 4, 9, 17, 49, 105, 244, 574, 1388, .... - _Robert G. Wilson v_, Dec 02 2013

%H Robert G. Wilson v, <a href="/A081763/b081763.txt">Table of n, a(n) for n = 1..1637</a>

%t Select[ Prime@ Range@ 6000, PowerMod[3, # - 1, # (# - 1)] == 1 &] (* _Robert G. Wilson v_, Dec 02 2013 *)

%o (PARI) lista(nn) = forprime(p=2, nn, if (! ((3^(p-1)-1) % (p*(p-1))), print1(p, ", "))) \\ _Michel Marcus_, Dec 02 2013

%o (PARI) is(n)=isprime(n) && Mod(3,n^2-n)^(n-1)==1 \\ _Charles R Greathouse IV_, Dec 02 2013

%K nonn

%O 1,1

%A _Benoit Cloitre_, Apr 09 2003

%E Missing term 2 added to sequence by _Robert G. Wilson v_, Dec 02 2013

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Last modified October 15 07:42 EDT 2019. Contains 328026 sequences. (Running on oeis4.)