Numbers k such that R_(k+2) + 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A256928
Numbers k such that R_(k+2) + 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =2a(2) =22a(3) =280a(4) =944a(5) =1376a(6) =1837a(7) =2329a(8) =2512a(9) =5186a(10) =24454a(11) =25354a(12) =49774a(13) =103474a(14) =159736a(15) =177754
External references
- oeis: A256928