Numbers k such that 10*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056655
Numbers k such that 10*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =1a(2) =3a(3) =4a(4) =7a(5) =22a(6) =28a(7) =39a(8) =130a(9) =135a(10) =214a(11) =610a(12) =766a(13) =2152a(14) =2575a(15) =22972a(16) =42688a(17) =85711a(18) =85863a(19) =112066a(20) =538507a(21) =631714
External references
- oeis: A056655