一.整数：integer，whole number
1.因子：factor or divisor
If x and y are integers and x≠0,x is a divisor (factor) of y provided that y=xn for some integer n. In this case y is also said to be divisible by x or to be a multiple of x. For example, 7 is a divisor or factor of 28 since 28=7 4, but 8 is not a divisor of 28 since there is no integer n such that 28=8n.Divisible adj.可以被整除的 multiple n.倍数
2.商和余数：quotients and remainders
余数和商都可以为0
3.奇数和偶数：odd and even integers
奇数和偶数都可以是负数;零一定是偶数
4.质数和合数：prime numbers and composite numbers
A prime number is a positive integer that has exactly two different positive divisors，1 and itself. For example, 2,3,5,7,11, and 13 are prime numbers, but 15 is not, since 15 has four different positive divisors, 1, 3, 5, and 15. The number 1 is not a prime number, since it has only one positive divisor. Every integer greater than 1 is either prime or can be uniquely expressed as a product of prime factors. For example, 14= (2) (7), 81= (3) (3) (3) (3), and 484= (2) (2) (11) (11).
注:GMAT考试除了1和其本身外,还有其他因子的数叫合数。GMAT数学最小的质数为2，最小的合数为4，在讨论质数和合数时，都指正数。1和0既不是质数，也不是合数。
5.整数中的重要概念：
* Perfect square完全平方数，诸如9 = 32
* Perfect cube 完全立方数，诸如8 = 23
* the greatest common divisor 最大公约数
GMAT入门几个数所公有的最大因子称最大公约数，诸如：48与36的公因子有1，2，3，4，6，12，其中12为最大公约数。
* the least common multiple最小公倍数
几个数所公有的最小倍数称最小公倍数，诸如：3，7和14的最小公倍数为42。
*连续正整数的算术平均值也是首项和末项的算术平均值。
同理，连续奇数与连续偶数的算术平均值也是首项和末项的算术平均值。
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