a(n) = 18*((10^n - 1)/9)^2.A178630a(n) = 18*((10^n - 1)/9)^2.Terms a(0) =18a(1) =2178a(2) =221778a(3) =22217778a(4) =2222177778a(5) =222221777778External referencesoeis: A178630