%I M5424 N2356 #29 Dec 12 2023 12:18:21
%S 251,571,971,1181,1811,2011,2381,2411,3221,3251,3301,3821,4211,4861,
%T 4931,5021,5381,5861,6221,6571,6581,8461,8501,9091,9461,10061,10211,
%U 10781,11251,11701,11941,12541,13171,13381,13421,13781,14251,15541,16091,16141,16451,16661,16691,16811,17291
%N Primes p such that the multiplicative order of 2 modulo p is (p-1)/5.
%D M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 1, p. 59.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H T. D. Noe, <a href="/A001135/b001135.txt">Table of n, a(n) for n = 1..1000</a>
%p q:= p-> isprime(p) and numtheory[order](2, p)=(p-1)/5:
%p select(q, [$2..20000])[]; # _Alois P. Heinz_, Dec 12 2023
%t Reap[For[p = 2, p <= 18000, p = NextPrime[p], If[ MultiplicativeOrder[2, p] == (p-1)/5, Sow[p]]]][[2, 1]] (* _James C. McMahon_, Dec 12 2023 *)
%o (Magma) [ p: p in PrimesUpTo(15541) | r eq 1 and Order(R!2) eq q where q,r is Quotrem(p,5) where R is ResidueClassRing(p) ]; // _Klaus Brockhaus_, Dec 02 2008
%o (PARI) forprime(p=3,10^5,if(znorder(Mod(2,p))==(p-1)/5,print1(p,", "))); \\ _Joerg Arndt_, May 17 2013
%Y Cf. A001133, A001134, A001136, A115586, A115591.
%K nonn
%O 1,1
%A _N. J. A. Sloane_
%E More terms and better definition from _Don Reble_, Mar 11 2006