Primes consisting only of digits 7 and 9 occurring with equal frequency.

Terms

a(0) =79a(1) =97a(2) =77997979a(3) =79779979a(4) =79797997a(5) =79997977a(6) =99977797a(7) =99979777a(8) =7777997999a(9) =7779799799a(10) =7779799997a(11) =7779979979a(12) =7797799979a(13) =7797979799a(14) =7799797799a(15) =7977799799a(16) =7979799977a(17) =7979979779a(18) =7979979797a(19) =7979979977a(20) =7979997797a(21) =7997799977a(22) =7997979779a(23) =7997997977