Rubin

The factors for 156 are 1, 2, 3, 4, 6, 12, 13, 26, 39, 52, 78, 156 grouped by last digit {1},{2, 12, 52},{3,13},{4},{6, 26, 156},{78},{39} Fenders are defined as factor enders. For example the fenders (factor enders) of 156 are 1, 2, 3, 4, 6, 8, 9 and that 156 is a 7-fender (that is, it has seven fenders). (Question 1) Show that a number which has 0 and 9 as fenders has at least four more fenders. (Question 2) The smallest 10-fender is less than 700. Find it and explain why it is the smallest.