2nd January 2026

AMM Problem 12548 Solution

Abstract Algebra: Counting a family of discrete functions

In this article, I provide the solution to AMM Problem 12548. This article is being published a day after the AMM deadline!
This is part of my December 31st 2025 deadline, of which I solved 5/7 problems that I'm sharing here! This is the 3rd such article.

This problem is about counting, for all nNn \in \mathbb{N}, the number of functions f:[n2][n]f: [n^2] \rightarrow [n] such that g:Z[n]\exists g: \mathbb{Z} \rightarrow [n] surjection such that for every a+ba+b even:

f(g(a),g(b))=g(a+b2) f(g(a), g(b)) = g(\frac{a+b}{2})

This problem taught me many interesting properties of medial operations. It's quite a lot of abstract algebra hidden in this problem. Despite the constraint appearing simple, it is very tricky to combine the several observations about f,gf,g into a whole proof.

I hope you enjoyed reading the article

Any feedback is greatly appreciated!

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