a(n) = 6*(10^(2*n+1)-1)/9 - 3*10^n.A332163a(n) = 6*(10^(2*n+1)-1)/9 - 3*10^n.Terms a(0) =3a(1) =636a(2) =66366a(3) =6663666a(4) =666636666a(5) =66666366666External referencesoeis: A332163