a(n) = 7*(10^(2*n+1) - 1)/9 - 5*10^n.A332172a(n) = 7*(10^(2*n+1) - 1)/9 - 5*10^n.Terms a(0) =2a(1) =727a(2) =77277a(3) =7772777a(4) =777727777a(5) =77777277777External referencesoeis: A332172