a(n) = (10^(2*n+1) - 1)/3 - 2*10^n.A332131a(n) = (10^(2*n+1) - 1)/3 - 2*10^n.Terms a(0) =1a(1) =313a(2) =33133a(3) =3331333a(4) =333313333a(5) =33333133333External referencesoeis: A332131