Primes p of the form 3k+1 such that -sqrt(p) < sum_{x=1..p} cos(2*Pi*x^3/p) < sqrt(p).

Terms

a(0) =13a(1) =19a(2) =37a(3) =61a(4) =109a(5) =157a(6) =193a(7) =241a(8) =283a(9) =367a(10) =373a(11) =379a(12) =397a(13) =487a(14) =571a(15) =613a(16) =619a(17) =733a(18) =739a(19) =859a(20) =883a(21) =907a(22) =1009a(23) =1033a(24) =1051a(25) =1129a(26) =1153a(27) =1201a(28) =1291a(29) =1297