An Interesting Combinatorics Problem

Revision en1, by AliRaging, 2026-10-03 07:19:13

In 2008, the American Mathematics Competition AMC 12 asked a simple question about heavy-tailed permutations of size 5. A heavy tail permutation of odd size n means that the first (n-1)/2 elements are less than the last (n-1)/2 elements. The problem is trivial for small size but proved to be difficult for me when trying to expand it to large n, which is why I ask for help after this blog in improving what I know so far.

If interested, here is the problem link and YouTube video explaining the problem:

2008 AMC 12A Problem 21 Video Explanation by Jaymin Shah

Tags combinatorics, math, i need help, permutations

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en7 English AliRaging 2026-10-03 08:16:58 0 (published)
en6 English AliRaging 2026-10-03 08:16:33 34 Tiny change: 'm!)^2\cdot&space;&hash;unique-of-combinatio' -> 'm!)^2\cdot#combinatio'
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en4 English AliRaging 2026-10-03 08:09:27 180
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en1 English AliRaging 2026-10-03 07:19:13 739 Initial revision (saved to drafts)