title: "IMO 1985 LL MOR54" description: "Set Sn = n" date: "2026-05-29T11:51:44+07:00" tags: ["imo", "longlist", "mathematics", "olympiad"] categories: ["mathematics"] year: 1985 type: "longlist" origin: "MOR" weight: 198500054 draft: false

IMO 1985 LL MOR54

Origin: MOR

Problem

Set Sn = n p=1(p5 + p7). Determine the greatest common divisor of Sn and S3n.