Divisible only by primes congruent to 3 mod 7.

Terms

a(0) =1a(1) =3a(2) =9a(3) =17a(4) =27a(5) =31a(6) =51a(7) =59a(8) =73a(9) =81a(10) =93a(11) =101a(12) =153a(13) =157a(14) =177a(15) =199a(16) =219a(17) =227a(18) =241a(19) =243a(20) =269a(21) =279a(22) =283a(23) =289a(24) =303a(25) =311a(26) =353a(27) =367a(28) =409a(29) =459