Numbers k such that 7*10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A103054
Numbers k such that 7*10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =3a(2) =4a(3) =7a(4) =9a(5) =13a(6) =33a(7) =37a(8) =76a(9) =147a(10) =297a(11) =1851a(12) =3457a(13) =3609a(14) =45219
External references
- oeis: A103054