Let , , , , be not necessarily distinct divisors of . Find all -permutations which satisfy the condition .
Mongolian Mathematical Olympiad
Solution
Let , , , , , be not necessarily distinct divisors of . First we will find number of -permutations that satisfy the condition .
Number of -permutations which satisfy the condition equals to number of -permutations which satisfy the condition . Number of -permutations with equals to . Therefore number of -permutations which satisfy the condition equals to .
Now we apply this result to the given problem. Setting we get and thus desired number is .
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