The sum of the squares of the first $$20$$ positive integers is $$2870$$. What is the sum of the squares of the first $$19$$ positive integers? 
Overseas Competition->Knowledge Point->Number Theory Modules->Perfect Square Numbers->Basic Applications of Square Numbers
The sum of the squares of the first $$20$$ positive integers is $$2870$$.  The sum of the squares of the first $$19$$ is $$2870-20^{2}=2870-400=2470$$. 