Primes having only {1, 2, 7} as digits.

Terms

a(0) =2a(1) =7a(2) =11a(3) =17a(4) =71a(5) =127a(6) =211a(7) =227a(8) =271a(9) =277a(10) =727a(11) =1117a(12) =1171a(13) =1217a(14) =1277a(15) =1721a(16) =1777a(17) =2111a(18) =2221a(19) =2711a(20) =2777a(21) =7121a(22) =7127a(23) =7177a(24) =7211a(25) =7717a(26) =7727a(27) =11117a(28) =11171a(29) =11177