Primes having only {1, 7, 9} as digits.

Terms

a(0) =7a(1) =11a(2) =17a(3) =19a(4) =71a(5) =79a(6) =97a(7) =179a(8) =191a(9) =197a(10) =199a(11) =719a(12) =797a(13) =911a(14) =919a(15) =971a(16) =977a(17) =991a(18) =997a(19) =1117a(20) =1171a(21) =1777a(22) =1979a(23) =1997a(24) =1999a(25) =7177a(26) =7717a(27) =7919a(28) =9199a(29) =9719