Wpb chapt2

Agree with @Utopia1138 about efficiency at low values, but Meh - I like the gratuitous use of Math! 
However, consider this story:
The reason I knew about the sqrt thing is I once set a competition where I asked for people to find the first  (I don't know... 1000?) primes, and to do it in the fastest program possible. One quy set an array containing all the primes (up to whatever) and then just iterated over it!