Numbers n such that 2*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A102954

Numbers n such that 2*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =3a(1) =9a(2) =15a(3) =21a(4) =27a(5) =87a(6) =180a(7) =1941a(8) =3960a(9) =4995a(10) =8577a(11) =23481a(12) =27855a(13) =80595

External references