Numbers k such that (31*10^k - 1)/3 is prime.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =7a(6) =8a(7) =12a(8) =18a(9) =30a(10) =75a(11) =140a(12) =212a(13) =1639a(14) =2167a(15) =4663a(16) =5526a(17) =8582a(18) =17636a(19) =19922a(20) =22470a(21) =90064a(22) =161582a(23) =288238