Numbers such that pre- and post-concatenating 7, 13 and 31 results in six primes.

Terms

a(0) =19a(1) =3583a(2) =11287a(3) =62989a(4) =63409a(5) =89491a(6) =93187a(7) =104107a(8) =106783a(9) =155851a(10) =178351a(11) =1082467a(12) =1219399a(13) =1510207a(14) =1566613a(15) =1581469a(16) =2246173a(17) =2920693a(18) =3081499a(19) =3342277a(20) =3523339a(21) =3781849a(22) =3820543a(23) =4010161a(24) =4824163a(25) =4865827a(26) =6091597