Numbers k such that k prefixed by '6' and followed by '7' is a prime.

Terms

a(0) =0a(1) =1a(2) =4a(3) =7a(4) =19a(5) =21a(6) =24a(7) =25a(8) =27a(9) =28a(10) =31a(11) =33a(12) =36a(13) =39a(14) =42a(15) =54a(16) =57a(17) =60a(18) =63a(19) =73a(20) =82a(21) =85a(22) =90a(23) =91a(24) =94a(25) =96a(26) =97a(27) =99a(28) =100a(29) =102