Numbers k such that 3*R_(k+2) + 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257025
Numbers k such that 3*R_(k+2) + 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =5a(4) =7a(5) =14a(6) =32a(7) =65a(8) =163a(9) =398a(10) =485a(11) =1799a(12) =1852a(13) =3326a(14) =3692a(15) =7226a(16) =12743a(17) =15313a(18) =110405a(19) =120395a(20) =132337a(21) =140357a(22) =153025a(23) =194150
External references
- oeis: A257025