Numbers k such that 4*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A056707

Numbers k such that 4*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =1a(1) =2a(2) =16a(3) =31a(4) =37a(5) =55a(6) =62a(7) =172a(8) =174a(9) =197a(10) =727a(11) =1246a(12) =1752a(13) =4318a(14) =4328a(15) =4930a(16) =6450a(17) =15206a(18) =24041a(19) =25321a(20) =33068a(21) =41484a(22) =51511

External references