Numbers k such that 30*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056680
Numbers k such that 30*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =5a(4) =45a(5) =393a(6) =977a(7) =2585a(8) =2810a(9) =2967a(10) =3641a(11) =4826a(12) =4917a(13) =5591a(14) =5705a(15) =10682a(16) =12890a(17) =14117a(18) =74349a(19) =88679
External references
- oeis: A056680