Practical numbers: Difference between revisions

This version has an optimisation that might prove ``much`` faster in some cases but slower than the above in others.

A number with a large number of factors, f has <code>2**len(f)</code> sets in its powerset. 672 for example has 23 factors and so 8_388_608 sets in its powerset.<br>

Just taking the sets as they are generated and stopping when we first know that 672 is Practical needs just the first 28_826 or 0.34% of

the sets. 720, another Practical number needs just 0.01% of its half a billion sets to prove it is Practical.

Note however that if the number is ```not```