Difference between revisions of "2018 UNCO Math Contest II Problems/Problem 11"

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{{UNCO Math Contest box|year=2018|n=II|num-b=10|after=Last Question}}
 
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[[Category: Intermediate Number Theory]]
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[[Category: Intermediate Number Theory Problems]]

Latest revision as of 00:36, 14 January 2019

Problem

(a) Find an integer $n > 1$ for which $1 + 2 + \ldots + n^2$ is a perfect square. (b) Show that there are infinitely many integers $n > 1$ that have the property that $1 + 2 + \ldots + n^2$ is a perfect square, and determine at least three more examples of such $n$. Hint: There is one approach that uses the result of a previous problem on this contest.

Solution

$7$ (Other acceptable answers are $41, 239, 1393, 8119$, and, in general, anything generated by the formula in part b. The answer students are most likely to give is $7$

See also

2018 UNCO Math Contest II (ProblemsAnswer KeyResources)
Preceded by
Problem 10
Followed by
Last Question
1 2 3 4 5 6 7 8 9 10
All UNCO Math Contest Problems and Solutions