Find the smallest positive integer for which there exist two distinct pairs of positive integers such that and .
Solution
Notice that for , the pairs and satisfy the condition.
We will show that for smaller numbers , there do not exist two distinct suitable pairs . If , then is not positive. Thus, we can assume that . Now, as or increases, also increases. Let's examine the cases.
* If , then give us respectively .
* If , then give similarly .
* If , then give .
No positive number smaller than 360 appeared repeatedly. If we continue the inspection for , even the first case would give , since gives 360 or a larger number for the same . In conclusion, 360 is the smallest number with the required property.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.