2011 UNCO Math Contest II Problems/Problem 2

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Problem

Let $m$ and $n$ be positive integers. List all the integers in the set $\left\{ 20 ,21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31\right\}$ that $\underline{cannot}$ be written in the form $m+n+m \cdot n$. As an example, $20$ $\underline{can}$ be so expressed since $20 = 2 + 6 + 2\cdot 6$.

Solution

$\{22,28,30\}$

See Also

2011 UNCO Math Contest II (ProblemsAnswer KeyResources)
Preceded by
Problem 1
Followed by
Problem 3
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All UNCO Math Contest Problems and Solutions
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