Numbers k such that 7*R_(k+2) - 2*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A257031

Numbers k such that 7*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) =5a(3) =10a(4) =11a(5) =16a(6) =23a(7) =247a(8) =1700a(9) =2891a(10) =3019a(11) =5549a(12) =5837a(13) =9326a(14) =14417a(15) =23312a(16) =24155a(17) =30740a(18) =61907a(19) =64421a(20) =69997a(21) =78656a(22) =163106a(23) =177266

External references