Palindromic primes with middle digit 7.

Terms

a(0) =7a(1) =373a(2) =12721a(3) =14741a(4) =30703a(5) =35753a(6) =38783a(7) =72727a(8) =74747a(9) =78787a(10) =90709a(11) =93739a(12) =96769a(13) =1117111a(14) =1177711a(15) =1257521a(16) =1287821a(17) =1317131a(18) =1327231a(19) =1407041a(20) =1437341a(21) =1447441a(22) =1557551a(23) =1597951a(24) =1657561a(25) =1707071a(26) =1737371a(27) =1777771a(28) =1917191a(29) =1957591