Undulating primes (digits alternate).

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =13a(5) =17a(6) =19a(7) =23a(8) =29a(9) =31a(10) =37a(11) =41a(12) =43a(13) =47a(14) =53a(15) =59a(16) =61a(17) =67a(18) =71a(19) =73a(20) =79a(21) =83a(22) =89a(23) =97a(24) =101a(25) =131a(26) =151a(27) =181a(28) =191a(29) =313