Primes having only {4, 7, 9} as digits.

Terms

a(0) =7a(1) =47a(2) =79a(3) =97a(4) =449a(5) =479a(6) =499a(7) =797a(8) =947a(9) =977a(10) =997a(11) =4447a(12) =4799a(13) =4999a(14) =7477a(15) =7499a(16) =7949a(17) =9479a(18) =9497a(19) =9749a(20) =9949a(21) =44449a(22) =44497a(23) =44777a(24) =44797a(25) =47497a(26) =47777a(27) =47779a(28) =47797a(29) =47947