Primes of the form XYYYYYX, where Y is a single digit.

Terms

a(0) =1333331a(1) =1444441a(2) =1777771a(3) =3222223a(4) =3444443a(5) =7666667a(6) =9222229a(7) =9888889a(8) =134444413a(9) =136666613a(10) =137777713a(11) =191111119a(12) =196666619a(13) =197777719a(14) =232222223a(15) =295555529a(16) =311111131a(17) =319999931a(18) =331111133a(19) =379999937a(20) =392222239a(21) =394444439