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

Terms

a(0) =2a(1) =4a(2) =6a(3) =10a(4) =12a(5) =14a(6) =17a(7) =41a(8) =69a(9) =141a(10) =170a(11) =188a(12) =204a(13) =233a(14) =306a(15) =555a(16) =743a(17) =1908a(18) =2006a(19) =2140a(20) =2772a(21) =8105a(22) =15170a(23) =40038a(24) =41908a(25) =48604a(26) =51652a(27) =54038a(28) =56781a(29) =129051