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

A331865

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

Terms

    a(0) =0a(1) =1a(2) =2a(3) =3a(4) =5a(5) =6a(6) =8a(7) =12a(8) =20a(9) =39a(10) =74a(11) =78a(12) =80a(13) =84a(14) =104a(15) =195a(16) =654a(17) =980a(18) =2076a(19) =5940a(20) =19637

External references