Numbers k such that k surrounded by digit '7' is prime.

Terms

a(0) =2a(1) =5a(2) =8a(3) =9a(4) =12a(5) =17a(6) =18a(7) =20a(8) =23a(9) =24a(10) =29a(11) =30a(12) =41a(13) =45a(14) =47a(15) =48a(16) =50a(17) =51a(18) =53a(19) =54a(20) =57a(21) =60a(22) =68a(23) =71a(24) =72a(25) =75a(26) =81a(27) =86a(28) =87a(29) =90