Numbers k such that (10^k - 1)/9 + 6 is prime.

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =8a(5) =23a(6) =29a(7) =40a(8) =131a(9) =136a(10) =215a(11) =611a(12) =767a(13) =2153a(14) =2576a(15) =22973a(16) =42689a(17) =85712a(18) =85864a(19) =112067a(20) =538508a(21) =631715