Numbers k such that 7*10^k + 2*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A103053
Numbers k such that 7*10^k + 2*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =4a(2) =12a(3) =13a(4) =15a(5) =36a(6) =40a(7) =90a(8) =837a(9) =2424a(10) =2427a(11) =2443a(12) =15925a(13) =16212
External references
- oeis: A103053