# 2019-19 Balancing consecutive squares

Find all integers $$n$$ such that the following holds:

There exists a set of $$2n$$ consecutive squares $$S = \{ (m+1)^2, (m+2)^2, \dots, (m+2n)^2 \}$$ ($$m$$ is a nonnegative integer) such that $$S = A \cup B$$ for some $$A$$ and $$B$$ with $$|A| = |B| = n$$ and the sum of elements in $$A$$ is equal to the sum of elements in $$B$$.

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# 2015-9 Sum of squares

Let $$n\ge 1$$ and $$a_0,a_1,a_2,\ldots,a_{n}$$ be non-negative integers. Prove that if $N=\frac{a_0^2+a_1^2+a_2^2+\cdots+a_{n}^2}{1+a_0a_1a_2\cdots a_{n}}$ is an integer, then $$N$$ is the sum of $$n$$ squares of integers.

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Find the smallest and the second smallest odd integers n satisfying the following property: $n=x_1^2+y_1^2 \text{ and } n^2=x_2^2+y_2^2$ for some positive integers $$x_1,y_1,x_2,y_2$$ such that $$x_1-y_1=x_2-y_2$$.