Smoothly undulating alternating primes.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =23a(5) =29a(6) =41a(7) =43a(8) =47a(9) =61a(10) =67a(11) =83a(12) =89a(13) =101a(14) =181a(15) =383a(16) =727a(17) =787a(18) =929a(19) =18181a(20) =32323a(21) =72727a(22) =74747a(23) =78787a(24) =94949a(25) =1212121a(26) =1616161a(27) =323232323a(28) =383838383a(29) =727272727