Primes that contain digits 7 and 9 only.

Terms

a(0) =7a(1) =79a(2) =97a(3) =797a(4) =977a(5) =997a(6) =77797a(7) =77977a(8) =77999a(9) =79777a(10) =79979a(11) =79997a(12) =79999a(13) =97777a(14) =777977a(15) =777979a(16) =779797a(17) =797977a(18) =799979a(19) =799999a(20) =999979a(21) =7777997a(22) =7779979a(23) =7779997a(24) =7797799a(25) =7797997a(26) =7799797a(27) =7799999a(28) =7977779a(29) =7977797