Numbers k such that 3*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A256375
Numbers k such that 3*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =4a(1) =5a(2) =6a(3) =8a(4) =13a(5) =14a(6) =25a(7) =30a(8) =44a(9) =58a(10) =383a(11) =455a(12) =463a(13) =504a(14) =511a(15) =1358a(16) =2293a(17) =4096a(18) =4374a(19) =8664a(20) =13676a(21) =23993a(22) =84134a(23) =90155a(24) =115794a(25) =127858
External references
- oeis: A256375