a(n) is 9 written in base 10-n.A001731a(n) is 9 written in base 10-n.Terms a(0) =9a(1) =10a(2) =11a(3) =12a(4) =13a(5) =14a(6) =21a(7) =100a(8) =1001a(9) =111111111External referencesoeis: A001731