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
combinatoricsSequencesEnumerative Combinatoricsnumber of ways