Primes of the concatenated form 7nn7.

Terms

a(0) =715157a(1) =718187a(2) =719197a(3) =734347a(4) =736367a(5) =739397a(6) =748487a(7) =752527a(8) =757577a(9) =760607a(10) =767677a(11) =775757a(12) =779797a(13) =781817a(14) =785857a(15) =796967a(16) =797977a(17) =7100510057a(18) =7102010207a(19) =7103010307a(20) =7104710477a(21) =7105410547a(22) =7106210627a(23) =7106510657a(24) =7107410747