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

Terms

a(0) =5a(1) =7a(2) =47a(3) =457a(4) =547a(5) =557a(6) =577a(7) =757a(8) =4447a(9) =4457a(10) =4547a(11) =5477a(12) =5557a(13) =7457a(14) =7477a(15) =7547a(16) =7577a(17) =7757a(18) =44777a(19) =45557a(20) =45757a(21) =47777a(22) =54547a(23) =54577a(24) =55457a(25) =55547a(26) =57457a(27) =57557a(28) =74747a(29) =75557