Repdigit - 1 is prime.

Terms

a(0) =3a(1) =4a(2) =6a(3) =8a(4) =44a(5) =444a(6) =888a(7) =2222a(8) =8888a(9) =444444a(10) =888888a(11) =444444444a(12) =888888888a(13) =444444444444a(14) =888888888888