Source: wikibot/rencontres-numbers
= Rencontres numbers
{wiki=Rencontres_numbers}
Rencontres numbers are a sequence of integers that arise in combinatorial mathematics, specifically in the context of permutations. They count the number of permutations of a set of \\( n \\) elements where exactly \\( k \\) elements are in their original (or "fixed") positions. The term "rencontre" comes from a French word meaning "meeting," reflecting the idea of elements meeting their original positions.