Numbers k such that (67*10^k - 7)/3 is prime.

Terms

a(0) =4a(1) =5a(2) =9a(3) =20a(4) =21a(5) =23a(6) =39a(7) =45a(8) =63a(9) =89a(10) =94a(11) =826a(12) =994a(13) =1054a(14) =2886a(15) =4829a(16) =5880a(17) =7928a(18) =17544a(19) =47277a(20) =93226a(21) =127413