Primes of the form identical digits followed by a 7.

Terms

a(0) =7a(1) =17a(2) =37a(3) =47a(4) =67a(5) =97a(6) =227a(7) =337a(8) =557a(9) =887a(10) =997a(11) =1117a(12) =4447a(13) =5557a(14) =8887a(15) =11117a(16) =333337a(17) =555557a(18) =666667a(19) =888887a(20) =11111117a(21) =66666667a(22) =222222227a(23) =666666667a(24) =888888887a(25) =4444444447a(26) =5555555557a(27) =66666666667a(28) =888888888887