www.mikescher.com/www/statics/euler/Euler_Problem-021_explanation.md

Most of the time is here spent in the NumberOfDivisors function. So we first cache every possible result of this function (from 0 to 10000).
The rest is simple searching for numbers where a == D(D(a)) and a != D(a).
	`Most of the time is here spent in the NumberOfDivisors function. So we first cache every possible result of this function (from 0 to 10000).`
	`The rest is simple searching for numbers where a == D(D(a)) and a != D(a).`