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PUMaC 2010 · 数论（B 组） · 第 2 题

PUMaC 2010 — Number Theory (Division B) — Problem 2

专题
Discrete Math / 离散数学
难度
L3
来源
PUMaC

题目详情

  1. Let f ( n ) be the sum of the digits of n . Find f ( n ). n =1 4 4
解析
  1. Let f ( n ) be the sum of the digits of n . Find f ( n ). n =1 9 ∑ Solution: The answer is 2 · 10 · i (2 for the number of digits, 10 for the number of times i =0 any digit appers in a place, and the sum for the sum of the 10 different digits), which is 900. 4 4