Odd primes p such that 21 is a square mod p.

Terms

a(0) =3a(1) =5a(2) =7a(3) =17a(4) =37a(5) =41a(6) =43a(7) =47a(8) =59a(9) =67a(10) =79a(11) =83a(12) =89a(13) =101a(14) =109a(15) =127a(16) =131a(17) =151a(18) =163a(19) =167a(20) =173a(21) =193a(22) =211a(23) =227a(24) =251a(25) =257a(26) =269a(27) =277a(28) =293a(29) =311