Numbers such that all the substrings of length <= 2 are primes.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =23a(5) =37a(6) =53a(7) =73a(8) =237a(9) =373a(10) =537a(11) =737a(12) =2373a(13) =3737a(14) =5373a(15) =7373a(16) =23737a(17) =37373a(18) =53737a(19) =73737a(20) =237373a(21) =373737a(22) =537373a(23) =737373a(24) =2373737a(25) =3737373a(26) =5373737a(27) =7373737a(28) =23737373a(29) =37373737