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PUMaC 2014 · 数论（B 组） · 第 2 题

PUMaC 2014 — 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. [ 3 ] What is the last digit of 17 ?
解析
  1. [ 3 ] What is the last digit of 17 ? Solution: 17 17 17 17 All we care is that 17 ≡ 1 ≡ 1 mod 4. Therefore, since the last digit repeats every four products of 17s, the last digit must be 7 .