Primes with either no internal digits or all internal digits are 7.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =11a(5) =13a(6) =17a(7) =19a(8) =23a(9) =29a(10) =31a(11) =37a(12) =41a(13) =43a(14) =47a(15) =53a(16) =59a(17) =61a(18) =67a(19) =71a(20) =73a(21) =79a(22) =83a(23) =89a(24) =97a(25) =173a(26) =179a(27) =271a(28) =277a(29) =373