Primes with exactly four 4's.

Terms

a(0) =44449a(1) =404449a(2) =440441a(3) =440443a(4) =441443a(5) =441449a(6) =442447a(7) =444043a(8) =444047a(9) =444341a(10) =444343a(11) =444347a(12) =444349a(13) =444401a(14) =444403a(15) =444421a(16) =444461a(17) =444463a(18) =444469a(19) =444473a(20) =444487a(21) =444547a(22) =444641a(23) =444649a(24) =444841a(25) =445447a(26) =446441a(27) =446447a(28) =447443a(29) =447449