digit-reduced numbers
Source: Bundeswettbewerb Mathematik 2006, round 2, problem 4
March 10, 2007
number theory unsolvednumber theory
Problem Statement
A positive integer is called digit-reduced if at most nine different digits occur in its decimal representation (leading s are omitted.) Let be a finite set of digit-reduced numbers. Show that the sum of the reciprocals of the elements in is less than .