Numbers n such that 4*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A102991

Numbers n such that 4*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =0a(1) =1a(2) =4a(3) =7a(4) =19a(5) =34a(6) =54a(7) =78a(8) =90a(9) =213a(10) =307a(11) =702a(12) =1456a(13) =2139a(14) =2214a(15) =3066a(16) =9300a(17) =16440a(18) =16894a(19) =28575a(20) =54051

External references