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PUMaC 2016 · 数论（B 组） · 第 5 题

PUMaC 2016 — Number Theory (Division B) — Problem 5

专题
Discrete Math / 离散数学
难度
L3
来源
PUMaC

题目详情

  1. For odd positive integers n , define f ( n ) to be the smallest odd integer greater than n that is not relatively prime to n . Compute the smallest n such that f ( f ( n )) is not divisible by 3.
解析
  1. Observe that if n is divisible by 3 then so is f ( n ). Thus, n and f ( n ) must not be divisible by