Primes of the form XYYX, where Y is a single digit.

Terms

a(0) =131113a(1) =137713a(2) =172217a(3) =178817a(4) =179917a(5) =191119a(6) =215521a(7) =233323a(8) =235523a(9) =271127a(10) =272227a(11) =278827a(12) =293329a(13) =313331a(14) =317731a(15) =319931a(16) =377737a(17) =392239a(18) =437743a(19) =472247a(20) =476647a(21) =491149a(22) =511151a(23) =512251a(24) =533353a(25) =571157a(26) =575557a(27) =577757a(28) =578857a(29) =599959