Primes obtained from other primes by pre-concatenating with 2.

Terms

a(0) =23a(1) =211a(2) =223a(3) =229a(4) =241a(5) =271a(6) =283a(7) =2113a(8) =2131a(9) =2137a(10) =2179a(11) =2239a(12) =2251a(13) =2269a(14) =2281a(15) =2293a(16) =2311a(17) =2347a(18) =2383a(19) =2389a(20) =2467a(21) =2503a(22) =2521a(23) =2557a(24) =2593a(25) =2617a(26) =2647a(27) =2659a(28) =2677a(29) =2683