Quote:
Originally Posted by R. Gerbicz
No, you need also that x1 and x2 are integers(!), and with this it is an integer optimization problem [without easy 'shortcuts"], you can try it out using say GLPK (it is free). And it is quite well known. Another similar form:
minimize 0
subject to:
x1 and x2 are integers
x1*x2=N
2<=x1
2<=x2
ps. note that if N is prime then this form has no solution.

Yes, exactly. I intended solution to be integers.
Also, I checked that integer optimization problems are NPcomplete in general, but I don't know if this particular problem is NPcomplete.