Indices k such that A020508(k)=Phi[k](-9) is prime, where Phi is a cyclotomic polynomial.

Terms

a(0) =3a(1) =9a(2) =12a(3) =15a(4) =20a(5) =27a(6) =33a(7) =36a(8) =59a(9) =69a(10) =91a(11) =152a(12) =207a(13) =223a(14) =232a(15) =264a(16) =336a(17) =340a(18) =380a(19) =381a(20) =492a(21) =533a(22) =540a(23) =547a(24) =549a(25) =585a(26) =615a(27) =624a(28) =627a(29) =720