Numbers k such that k prefixed by '2' and followed by '7' is prime.

Terms

a(0) =2a(1) =5a(2) =7a(3) =13a(4) =20a(5) =23a(6) =26a(7) =28a(8) =29a(9) =34a(10) =35a(11) =37a(12) =41a(13) =43a(14) =44a(15) =46a(16) =47a(17) =55a(18) =61a(19) =64a(20) =65a(21) =67a(22) =68a(23) =70a(24) =76a(25) =77a(26) =79a(27) =83a(28) =85a(29) =88