Numbers k such that 10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A089147
Numbers k such that 10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =3a(2) =9a(3) =13a(4) =42a(5) =51a(6) =54a(7) =91a(8) =120a(9) =168a(10) =510a(11) =819a(12) =1071a(13) =1756a(14) =3010a(15) =4333a(16) =9534a(17) =17839a(18) =114846
External references
- oeis: A089147