Problem of the Week 1185
Let N be an integer whose decimal digits from left to right are
nondecreasing (e.g., 113445889) and having distinct digits as its two
rightmost digits. Let s be the sum of the digits of 9N. Then s is divisible
by 9, so
How large can M be?
Source: Felix Lazebnik, Surprises, Math Mag. 87 (2014) 212-221.
© Copyright 2014 Stan Wagon. Reproduced with permission.