n = 21857711 nums = str(n) length = len(nums) count = 0 i = 0 #统计n位数中满足情况的个数,逐位遍历 for char in nums: num = int(char) i += 1 if num < 4: break if num > 4 and num < 7: count += pow(2, (length - i)) break if num > 7: count += pow(2, (le...