Benchmark: timing 100000 iterations of loop, recursion...
      loop:  6 wallclock secs ( 5.30 usr +  0.00 sys =  5.30 CPU) @ 18867.92/s (n=100000)
 recursion:  6 wallclock secs ( 5.87 usr +  0.00 sys =  5.87 CPU) @ 17035.78/s (n=100000)