Primes having only {2, 4, 7} as digits.

Terms

a(0) =2a(1) =7a(2) =47a(3) =227a(4) =277a(5) =727a(6) =2447a(7) =2477a(8) =2777a(9) =4447a(10) =7247a(11) =7477a(12) =7727a(13) =22247a(14) =22277a(15) =22447a(16) =22727a(17) =22777a(18) =24247a(19) =27277a(20) =27427a(21) =42227a(22) =42727a(23) =44777a(24) =47777a(25) =72227a(26) =72277a(27) =72727a(28) =74747a(29) =77447