a(n) = (1/9)*(10^(2*n) + 10^n - 2).A181718a(n) = (1/9)*(10^(2*n) + 10^n - 2).Terms a(0) =0a(1) =12a(2) =1122a(3) =111222a(4) =11112222a(5) =1111122222a(6) =111111222222External referencesoeis: A181718