a(n) = 10^(2*n) + 10^n + 1.A066138a(n) = 10^(2*n) + 10^n + 1.Terms a(0) =3a(1) =111a(2) =10101a(3) =1001001a(4) =100010001a(5) =10000100001External referencesoeis: A066138