OFFSET
1,1
COMMENTS
2 is counted with the primes 1 (mod 4) because it is a frequent prime primitive root and primes (1,2) (mod 4) together build sequence A002313.
EXAMPLE
31 has primitive roots 3, 11, 12, 13, 17, 21, 22, 24, ...;
13 and 17 are primes 1 (mod 4), count is 2;
3 and 11 are primes 3 (mod 4), count is 2;
thus 31 is a term of this sequence.
MATHEMATICA
q[n_] := Module[{p = Select[PrimitiveRootList[n], PrimeQ], m}, m = Length[p]; m > 0 && EvenQ[m] && Length @ Select[p, Mod[#, 4] == 3 &] == m/2]; Select[Range[2700], q] (* Amiram Eldar, Aug 26 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Sven Simon, Aug 31 2004
EXTENSIONS
Offset 1 and name edited by Michel Marcus, Aug 25 2021
STATUS
approved