Numbers n such that 2*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

A102957

Numbers n such that 2*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Terms

    a(0) =0a(1) =1a(2) =2a(3) =4a(4) =7a(5) =14a(6) =20a(7) =39a(8) =102a(9) =156a(10) =457a(11) =1190a(12) =2308a(13) =5870a(14) =8314a(15) =9703a(16) =12828a(17) =14959a(18) =17995a(19) =19730a(20) =26480a(21) =31440

External references