求50以内有6个约数有哪些?
2个回答
去掉所有的质数:
2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
去掉几个平方数:1,4,9,25,49
这样还有 30个数字
去掉11的倍数:22,33,44
去掉13的倍数:26,39
去掉17,19,23的倍数:34,38,46
去掉三次方数:8,27
还有20个数字:6,10,12,14,15,16,18,20,21,24,28,30,32,35,36,40,42,45,48,50
其中,6,10,14,15,21,35只有四个约数
还剩下16个
12:1,2,3,4,6,12
16:1,2,4,8,16
18:1,2,3,6,9,18
20:1,2,4,5,10,20
24:1,2,3,4,6,8,12,24
28:1,2,4,7,14,28
30:1,2,4,8,16,32
36:1,2,3,4,6,9,12,18,36
40:1,2,4,5,8,10,20,40
42:1,2,3,6,7,14,21,42
45:1,3,5,9,15,45
48:1,2,3,4,6,8,12,16,24,48
50:1,2,5,10,25,50
因此,合乎规定的有12,18,20,28,30,45,50等7个数字.
