a(n) = 7*(10^(2n+1)-1)/9 - 3*10^n.A332174a(n) = 7*(10^(2n+1)-1)/9 - 3*10^n.Terms a(0) =4a(1) =747a(2) =77477a(3) =7774777a(4) =777747777a(5) =77777477777External referencesoeis: A332174