Omar Khayyam (1048-1131) |

Find all values of n such that S(n) = 120 and prove that there are no others.

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In most countries, mathematics competitions tend to be multiple-choice answers in the first round, then numerical answers in the follow-up round. But if you make it beyond these rounds, the questions become longer and harder and you will need to show your full solutions.

Finding an answer is sometimes the easiest part; showing that you have found all the answers is often the hardest part. With this in mind, it is worth doing the above question by hand as it will also be the way you can show that you have found all the solutions.

Enjoy!

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