Numbers k such that 9*R_(k+2) - 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A257039

Numbers k such that 9*R_(k+2) - 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =10a(1) =12a(2) =63a(3) =69a(4) =156a(5) =328a(6) =340a(7) =344a(8) =444a(9) =672a(10) =894a(11) =1464a(12) =1670a(13) =1708a(14) =2010a(15) =4306a(16) =7888a(17) =8864a(18) =9478a(19) =9621a(20) =26004a(21) =36992a(22) =71600a(23) =98738a(24) =118949a(25) =130565a(26) =140326a(27) =183452a(28) =211983a(29) =225618

External references