Numbers n such that 8*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A103080

Numbers n such that 8*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =0a(1) =1a(2) =3a(3) =4a(4) =10a(5) =15a(6) =25a(7) =69a(8) =159a(9) =166a(10) =261a(11) =442a(12) =1339a(13) =1797a(14) =2170a(15) =3163a(16) =3472a(17) =4917a(18) =18267

External references