Numbers k such that 3*R_(k+2) + 2*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A256788

Numbers k such that 3*R_(k+2) + 2*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =1a(1) =2a(2) =4a(3) =16a(4) =23a(5) =25a(6) =27a(7) =29a(8) =34a(9) =68a(10) =89a(11) =127a(12) =200a(13) =418a(14) =868a(15) =1173a(16) =2553a(17) =4131a(18) =5675a(19) =8318a(20) =8445a(21) =10820a(22) =15793a(23) =16671a(24) =32275a(25) =43995a(26) =48026a(27) =50035a(28) =88459a(29) =126839

External references