Primes having only {0, 4, 7} as digits.

Terms

a(0) =7a(1) =47a(2) =4007a(3) =4447a(4) =7477a(5) =44777a(6) =47407a(7) =47777a(8) =74047a(9) =74077a(10) =74707a(11) =74747a(12) =77047a(13) =77447a(14) =77477a(15) =77747a(16) =407047a(17) =407707a(18) =407747a(19) =440047a(20) =444007a(21) =444047a(22) =470077a(23) =470447a(24) =474077a(25) =474707a(26) =477047a(27) =477077a(28) =704447a(29) =704477