Numbers n such that 5*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A103019

Numbers n such that 5*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =2a(1) =6a(2) =9a(3) =27a(4) =30a(5) =48a(6) =141a(7) =150a(8) =372a(9) =422a(10) =1097a(11) =3570a(12) =4607a(13) =5289a(14) =10734a(15) =11550a(16) =32604a(17) =42470a(18) =46311a(19) =67578

External references