关于阶乘的How many seven-digit telephone numbers are there for any one area code if the numbers 0 or 1 can not be used as the first digit of a seven digit phone number?
问题描述：
关于阶乘的
How many seven-digit telephone numbers are there for any one area code if the numbers 0 or 1 can not be used as the first digit of a seven digit phone number?
答
不用阶乘啊…… 第一位不能用0、1,所以有8种组合.后面6位每位有10种组合,一共是8*10^6=8,000,000