Abstract :
[en] Let $\bfx = (x_0,\ldots,x_{n-1})$ be an $n$-chain, i.e., an $n$-tuple of non-negative integers $< n$. Consider the operator $s: \bfx \mapsto\bfx' = (x'_0,\ldots,x'_{n-1})$, where $x'_j$ represents the number of $j$'s appearing among the components of $\bfx$. An $n$-chain $\bfx$ is said to be perfect if $s(\bfx) = \bfx$. For example, (2,1,2,0,0) is a perfect 5-chain. Analogously to the theory of perfect, amicable, and sociable numbers, one can define from the operator $s$ the concepts of amicable pair and sociable group of chains. In this paper we give an exhaustive list of all the perfect, amicable, and sociable chains.
