A255207 - OEIS

%I #8 Mar 07 2015 15:33:37

%S 487,1163,2203,2731,3373,4391,5261,6343,6451,6569,7753,8377,8863,9041,

%T 9397,9463,9941,10079,10321,11783,12703,13121,13151,13807,13903,14419,

%U 15061,15263,15313,15601,16631,16883,16943,17477,17519,18253,18773,20173,22279,23291

%N Primes p for which exactly four bases b with 1 < b < p exist such that p is a base b Wieferich prime.

%C p = prime(n) such that A242830(n) = 4.

%o (PARI) forprime(p=1, , b=2; i=0; while(b < p, if(Mod(b, p^2)^(p-1)==1, i++); b++); if(i==4, print1(p, ", ")))

%Y Cf. A255203, A255204, A255205, A255206, A255208, A255209, A255210.

%K nonn

%O 1,1

%A _Felix Fröhlich_, Feb 17 2015