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Sum three, get one (Posted on 2007-04-25) |
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Determine all possible positive integer solutions of this equation:
n! = a! + b! + c!
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Submitted by K Sengupta
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Rating: 2.5000 (2 votes)
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Solution:
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(Hide)
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If possible, let n < = a, b, c Then, a! + b! + c! > = 3n > n, a contradiction. Thus, n > a, b, c
If in addition, n > 3, then:
n! > 3 (n-1)! > = a! + b! + c!. This is a contradiction
Accordingly, it follows that: n = 1, 2, or 3.
A check for these values of n, yields:
3! = 2! + 2! + 2!.
Hence n =3; a=b=c =2 is the only possible solution to the given problem.
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