Primes having only {4, 5, 6, 7} as digits.

Terms

a(0) =5a(1) =7a(2) =47a(3) =67a(4) =457a(5) =467a(6) =547a(7) =557a(8) =577a(9) =647a(10) =677a(11) =757a(12) =4447a(13) =4457a(14) =4547a(15) =4567a(16) =4657a(17) =5477a(18) =5557a(19) =5647a(20) =5657a(21) =6547a(22) =6577a(23) =7457a(24) =7477a(25) =7547a(26) =7577a(27) =7757a(28) =44647a(29) =44657