[seqfan] a Diophantine equation

David Newman davidsnewman at gmail.com
Wed Nov 12 03:09:04 CET 2008


A student,  named Daniel Reichman, asked this question.

Suppose that a,b, and c, integers, satisfy

a^2+b^2= c^2.

For which n are there a,b such that 2ab=n!  ?

He notes that there are at least three solutions:

For n=4, a=4, b=3
For n=5  a=12, b=5
For n=6, a=40, b=9

Are there any other such n?



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