Primes having only {2, 7, 9} as digits.

Terms

a(0) =2a(1) =7a(2) =29a(3) =79a(4) =97a(5) =227a(6) =229a(7) =277a(8) =727a(9) =797a(10) =929a(11) =977a(12) =997a(13) =2297a(14) =2729a(15) =2777a(16) =2797a(17) =2927a(18) =2999a(19) =7229a(20) =7297a(21) =7727a(22) =7927a(23) =9227a(24) =9277a(25) =9929a(26) =22229a(27) =22277a(28) =22279a(29) =22727