Substrings from the right are prime numbers (using only odd digits different from 5).

Terms

a(0) =3a(1) =7a(2) =13a(3) =17a(4) =37a(5) =73a(6) =97a(7) =113a(8) =137a(9) =173a(10) =197a(11) =313a(12) =317a(13) =337a(14) =373a(15) =397a(16) =773a(17) =797a(18) =937a(19) =997a(20) =1373a(21) =1997a(22) =3137a(23) =3313a(24) =3373a(25) =3797a(26) =7937a(27) =9137a(28) =9173a(29) =9337