Numbers k such that R_k + 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A256722

Numbers k such that R_k + 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =2a(1) =3a(2) =5a(3) =8a(4) =9a(5) =11a(6) =18a(7) =20a(8) =29a(9) =39a(10) =123a(11) =153a(12) =267a(13) =327a(14) =627a(15) =1020a(16) =1686a(17) =1764a(18) =2960a(19) =18236a(20) =34613a(21) =53991a(22) =67404a(23) =119880a(24) =221654a(25) =230706

External references