Numbers k such that k concatenated with k+2 is a prime.

Terms

a(0) =1a(1) =7a(2) =9a(3) =27a(4) =37a(5) =45a(6) =49a(7) =51a(8) =55a(9) =61a(10) =69a(11) =75a(12) =105a(13) =109a(14) =115a(15) =117a(16) =121a(17) =151a(18) =159a(19) =181a(20) =187a(21) =195a(22) =201a(23) =211a(24) =217a(25) =225a(26) =247a(27) =271a(28) =277a(29) =285