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Found problems: 1

2000 Saint Petersburg Mathematical Olympiad, 11.3
Tags: enumerative combinatorics , number of ways , sequence , combinatorics
Every month a forester Ermolay has planted 2000 trees along a fence. On every tree, he has written how many oaks there are among itself and trees at his right and left. This way a sequence of 2000 numbers was created. How many distinct sequences could the forester Ermolay get? (oak is a certain type of tree) [I]Proposed by A. Khrabrov, D.Rostovski[/i]