What is the least positive integer that is not a factor of 25! and is not a prime number?
A. 26
B. 28
C. 36
D. 56
E. 58
解答：25!指的是 25 阶乘=25*24*...*1
5 显然是 factor
6,7,8,9,10,...,25 显然都是 factor
26=2*13 也是
27=3*3*3， 25!中有 3 和 9，所以也是 factor
28=4*7,factor
29 是 prime
30=3*10
31prime
32=4*8,factor
33=3*11,factor
34=2*17,factor
35=5*7,factor
36=4*9,factor
37prime
38=2*19,factor
39prime
40=4*10,factor
41prime
42=2*21factor
43prime
44=4*11factor
45=5*9factor
46=2*23factor
47prime
48=6*8factor
49=7*7,25!包含 7 和 14， factor
50=5*10factor
51=3*17factor
52=4*13factor
53prime
54=2*3*9,factor
55=5*11,factor
56=7*8,factor
57=3*19,factor
58=2*29,not a factor and not a prime
所以 58 is the least positive integer that is not a factor of 25! and is not a prime number.