Primes that are the concatenation of x, 1 and x for some x.

Terms

a(0) =313a(1) =919a(2) =17117a(3) =21121a(4) =27127a(5) =29129a(6) =39139a(7) =41141a(8) =47147a(9) =51151a(10) =59159a(11) =71171a(12) =81181a(13) =87187a(14) =89189a(15) =1131113a(16) =1171117a(17) =1191119a(18) =1311131a(19) =1371137a(20) =1411141a(21) =1591159a(22) =1611161a(23) =1771177a(24) =1891189a(25) =2011201a(26) =2391239a(27) =2631263a(28) =2871287a(29) =2911291