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%I #25 Apr 29 2024 09:30:10
%S 11,37,41,53,79,83,107,173,227,239,271,317,347,359,467,479,563,587,
%T 643,719,733,773,797,839,907,1031,1187,1231,1283,1307,1319,1439,1493,
%U 1523,1627,1637,1879,1907,1987,2027,2039,2467,2477,2677,2791,2837,2879,2963
%N Primes p for which the period of 1/p is prime.
%C Primes p such that the multiplicative order of 10 (mod p) is prime. - _Joerg Arndt_, Oct 26 2014
%C Together with 3, complement in primes of A249330. - _Arkadiusz Wesolowski_, Oct 25 2014
%H Ray Chandler, <a href="/A072859/b072859.txt">Table of n, a(n) for n = 1..10000</a>
%e 1/37 = 0. 027 027 ... with period = 3, hence 37 is in the sequence.
%t Select[Prime[Range[500]],PrimeQ[MultiplicativeOrder[10,#]]&] (* _Ray Chandler_, Oct 31 2011 *)
%o (PARI) f(n)=if(n<4,n==2,znorder(Mod(10, prime(n))));
%o for(n=1,100,if(isprime(f(n))==1,print1(prime(n),", ")))
%Y Cf. A002371, A249330.
%K base,easy,nonn
%O 1,1
%A _Benoit Cloitre_, Jul 26 2002