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

A102953

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

Terms

    a(0) =1a(1) =4a(2) =7a(3) =12a(4) =30a(5) =94a(6) =178a(7) =196a(8) =564a(9) =1801a(10) =3520a(11) =3538a(12) =8233a(13) =35161a(14) =37405a(15) =42330a(16) =70051a(17) =90792a(18) =124096a(19) =152670

External references