10000000改进函数
(define (find-devisor n test-devisor)
(cond ((> (square test-devisor) n) n)
((divides? test-devisor n) test-devisor)
(else (find-devisor n (next test-devisor)))))
(define (next n)
(if (= n 2)
3
(+ n 2)))
10000000 times 1000
---------------------
10000019 0.341
10000079 0.343
10000103 0.342
100000000 times 1000
---------------------
100000007 1.079
100000037 1.048
100000039 1.035
1000000000 times 500
---------------------
1000000007 3.708
1000000009 3.692
1000000021 3.81
10000000000 times 250
---------------------
10000000019 12.088
10000000033 11.94
10000000061 11.956
100000000000 times 100
---------------------
100000000003 37.91
100000000019 38.44
100000000057 38.14
1000000000000 times 30
---------------------
1000000000039 118.967
1000000000061 121.333
1000000000063 118.9
10000000000000 times 10
----------------------
10000000000037 386.7
10000000000051 384.5
10000000000099 385.8
用上面的结果列表：
| num | avg-1 | avg-2 | ratio-1 | ratio-2 | avg-1/avg-2 |
| 10000000 | 0.5523 | 0.345 | / | / | 1.601 |
| 100000000 | 1.741 | 1.054 | 3.152 | 3.055 | 1.652 |
| 1000000000 | 6.14 | 3.737 | 3.527 | 3.546 | 1.643 |
| 10000000000 | 20.453 | 11.995 | 3.331 | 3.210 | 1.705 |
| 100000000000 | 65.4 | 38.163 | 3.198 | 3.182 | 1.714 |
| 1000000000000 | 208.3 | 119.733 | 3.180 | 3.137 | 1.740 |
| 10000000000000 | 655.167 | 385.667 | 3.145 | 3.221 | 1.699 |
可以看到比值并不是2，一个直观的解释是我们定义的next是一个函数，对一个数的检测要调用next√n / 2 次，造成以一定的开销损耗。可以观察到，其实我们找出来的素数都是奇数，也就不需要为2单独判断，于是可以把next函数改为(+ test-divisor 2)，再进行一次实验。
10000000 times 1000
---------------------
10000019 0.276
10000079 0.275
10000103 0.282
100000000 times 1000
---------------------
100000007 0.866
100000037 0.868
100000039 0.868
1000000000 times 500
---------------------
1000000007 3.054
1000000009 3.084
1000000021 3.058
10000000000 times 250
---------------------
10000000019 9.956
10000000033 10.292
10000000061 10.18
100000000000 times 100
---------------------
100000000003 32.36
100000000019 33.35
100000000057 32.49
1000000000000 times 30
---------------------
1000000000039 101.333
1000000000061 103.4
1000000000063 102.433
10000000000000 times 10
----------------------
10000000000037 319.6
10000000000051 331.1
10000000000099 341.9
| num | avg-1 | avg-2* | ratio-1 | ratio-2* | avg-1/avg-2* |
| 10000000 | 0.5523 | 0.277 | / | / | 1.994 |
| 100000000 | 1.741 | 0.867 | 3.152 | 3.130 | 2.008 |
| 1000000000 | 6.14 | 3.065 | 3.527 | 3.535 | 2.003 |
| 10000000000 | 20.453 | 10.143 | 3.331 | 3.309 | 2.016 |
| 100000000000 | 65.4 | 32.733 | 3.198 | 3.227 | 1.998 |
| 1000000000000 | 208.3 | 102.389 | 3.180 | 3.128 | 2.034 |
| 10000000000000 | 655.167 | 330.867 | 3.145 | 3.231 | 1.980 |
可以看到调整之后的比例基本都在2的附近，所以可以肯定损耗的原因是next函数带来的开销了。