Primes that are either single-digit primes or a concatenation of two earlier terms.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =23a(5) =37a(6) =53a(7) =73a(8) =223a(9) =233a(10) =337a(11) =353a(12) =373a(13) =523a(14) =733a(15) =773a(16) =2237a(17) =2333a(18) =3373a(19) =3533a(20) =3733a(21) =5233a(22) =5237a(23) =5323a(24) =7333a(25) =7523a(26) =23333a(27) =23773a(28) =25237a(29) =32237