Problem 172 题目发布于 2007-12-15 翻译更新于 2015-10-20 Problem 172 Investigating numbers with few repeated digits How many 18-digit numbers n (without leading zeros) are there such that no digit occurs more than three times in n? 关于有少量重复数字的数的研究 有多少个18位数n（不考虑前导零）满足在n中没有一个数字出现超过三次？