Indices k such that A020507(k)=Phi[k](-8) is prime, where Phi is a cyclotomic polynomial.

Terms

a(0) =6a(1) =15a(2) =18a(3) =21a(4) =39a(5) =69a(6) =159a(7) =165a(8) =174a(9) =231a(10) =378a(11) =408a(12) =501a(13) =504a(14) =606a(15) =873a(16) =897a(17) =1122a(18) =1209a(19) =1395a(20) =1947a(21) =2040a(22) =2361a(23) =2778a(24) =3369a(25) =7305a(26) =7647a(27) =8154a(28) =8331a(29) =9483