Find all finite sequences such that for every , , equals the number of times appears in the sequence.
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Find all finite sequences $(x_0, x_1, \ldots,x_n)$ such that for every $j$, $0 \leq j \leq n$, $x_j$ equals the number of times $j$ appears in the sequence.
Izvor: Međunarodna matematička olimpijada, shortlist 2001
Školjka 
such that for every 
, 
, 
equals the number of times