Time comparison to enumerate all primes less than or equal to 999997:

   Method of enumeration                         Elapsed Time (seconds)
   ---------------------                         ---------------------- 
Version 0  (No sieve at all; sqrt(N) divisions)        13.90

Version 4  (Rebuild the sieve N-2 times)              198.24 

Version 4a (Extend the sieve incrementally)             8.22

Version 5  (Build just one big sieve)                   1.91

Version pRec2  (Tabulating recursion)                   8.51