Numbers k such that 3*R_(k+2) + 5*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257026
Numbers k such that 3*R_(k+2) + 5*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =2a(2) =3a(3) =9a(4) =10a(5) =13a(6) =19a(7) =25a(8) =33a(9) =124a(10) =150a(11) =175a(12) =199a(13) =290a(14) =301a(15) =506a(16) =592a(17) =1016a(18) =1459a(19) =4150a(20) =6396a(21) =7059a(22) =8311a(23) =8355a(24) =8811a(25) =13200a(26) =13270a(27) =26775a(28) =33303a(29) =62073
External references
- oeis: A257026