根据任何规律对于每一个自然数 n=1,2,3,……,给对应一个,可随 n 而异的,确定的数 a_n(我们可限于实数),这样就得着一个数列。因此数列无非是函数的特例——以全体自然数为定义域的函数。如所周知,对应于 n 的函数值叫做这数列的第 n 项。如果将 a_1写在第一位,a_2写在第二位,……那么,一个数列总可以写成 According to any law, for each natural number n=1, 2, 3,..., there is a corresponding number, which can vary with n, the determined number a_n (we can be limited to real numbers), so that we have a series. So a sequence is nothing more than a special case of a function—a function that defines the domain by its natural number. As we all know, the function value corresponding to n is called the nth item of this series. If you write a_1 in the first place, a_2 is written in the second place... Then, a sequence can always be written as