Numbers n for which R(n) + 4*10^floor(n/2) is prime, where R(n) = (10^n-1)/9 (repunit: A002275).

A331869

Numbers n for which R(n) + 4*10^floor(n/2) is prime, where R(n) = (10^n-1)/9 (repunit: A002275).

Terms

    a(0) =1a(1) =3a(2) =4a(3) =15a(4) =76a(5) =91a(6) =231a(7) =1363a(8) =1714a(9) =1942a(10) =2497a(11) =4963a(12) =5379a(13) =12397a(14) =23224a(15) =26395

External references