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PUMaC 2010 · 数论（A 组） · 第 1 题

PUMaC 2010 — Number Theory (Division A) — Problem 1

专题
Discrete Math / 离散数学
难度
L3
来源
PUMaC

题目详情

  1. Find the smallest positive integer n such that n + ( n + 1) is composite.
解析
  1. Find the smallest positive integer n such that n + ( n + 1) is composite. Solution: One can check that 17, 97, 337, and 881 are prime, and also that 17 · 113 = 1921, so the answer is 5.