Numbers n such that 4*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A102985

Numbers n such that 4*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =0a(1) =1a(2) =4a(3) =9a(4) =10a(5) =31a(6) =70a(7) =160a(8) =171a(9) =277a(10) =630a(11) =724a(12) =3717a(13) =5542a(14) =5634a(15) =10656a(16) =12724a(17) =31954

External references