Interesting question
David Wilson
dwilson at gambitcomm.com
Mon Aug 18 18:02:01 CEST 2008
Yes, that neatly solves the problem.
I started out looking at what numbers were not of the form xy+yz+zx for
positive integers, which turns out to be a hard problem (it's A025052 +
possibly one other very large term). Naturally, I went on to check
numbers not of the from wx+xy+yz+zw, and was surprised to see the 1 and
the primes. The factorization makes the solution trivial. The
interesting thing, i guess, is that a factorization exists only for a
4-term expression of this sort.
So on to five terms.
Azarian, Mohammad K. wrote:
> Is it helpful to say that which integers are of the form mn=(x+z)(w+y)?
>
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