Those are some nifty numbers
Number Theory
Level
5
For each positive integer \(n\), let \(s(n)\) denote the sum of the digits of \(n\). We call a number nifty if it can be expressed as \(n-s(n)\) for some positive integer \(n\).
How many positive integers less than 10 000 are nifty?
by
Sharky Kesa