%N Integers i > 1 for which there are three primes p such that i is a solution mod p of x^4 = 2.
%C Solutions mod p are represented by integers from 0 to p-1. The following equivalences holds for i > 1: There is a prime p such that i is a solution mod p of x^4 = 2 iff i^4 - 2 has a prime factor > i; i is a solution mod p of x^4 = 2 iff p is a prime factor of i^4 - 2 and p > i. i^4 - 2 has at most three prime factors > i. For i such that i^4 - 2 has no resp. one resp. two prime factors > i cf. A065903 resp. A065904 resp. A065905.
%F a(n) = n-th integer i such that i^4 - 2 has three prime factors > i.
%e a(3) = 55, since 55 is (after 15 and 48) the third integer i for which there are three primes p > i (viz. 73, 103 and 1217) such that i is a solution mod p of x^4 = 2, or equivalently, 55^4 - 2 = 9150623 = 73*103*1217 has three prime factors > 4. (cf. A065902).
%o (PARI): a065906(m) = local(c,n,f,a,s,j); c = 0; n = 2; while(c<m,f = factor(n^4-2); a = matsize(f); s = ; for(j = 1,a, if(f[j,1]>n,s = concat(s,f[j,1]))); if(matsize(s) == 3,print1(n,","); c++); n++) a065906(50)
%Y Cf. A040028, A065902, A065903, A065904, A065905.
%A _Klaus Brockhaus_, Nov 28 2001