Why is $1$ not a prime number? - Mathematics Stack Exchange 50 actually 1 was considered a prime number until the beginning of 20th century Unique factorization was a driving force beneath its changing of status, since it's formulation is quickier if 1 is not considered a prime; but I think that group theory was the other force
为什么 1 不能被认为是质数？ - 知乎 m = p 1 a 1 p 2 a 2 p 3 a 3 p n a n 什么意思呢？ 它表示这样一个结论：对于任意的一个整数，你都能把它因数分解，而且结果是唯一的。 举个例子：1001只能被分解成7×11×13，而且你再也找不到除 (7,11,13)外的一组质数，使它们的乘积是1001。 那么这个定理有什么用呢？