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COMMENTS
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An anti-run is a sequence with no adjacent equal parts. For example, the maximal anti-runs in (3,1,1,2,2,2,1) are ((3,1),(1,2),(2),(2,1)). In general, there is one more maximal anti-run than the number of pairs of adjacent equal parts.
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EXAMPLE
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The a(4) = 24 sequences:
(2,1,2,2) (2,1,3,3) (3,1,2,2)
(2,2,1,2) (2,3,3,1) (3,2,2,1)
(1,2,2,1) (3,3,1,2) (1,1,2,3)
(2,1,1,2) (3,3,2,1) (1,1,3,2)
(1,1,2,1) (1,2,2,3) (2,1,1,3)
(1,2,1,1) (1,3,2,2) (2,3,1,1)
(1,2,3,3) (2,2,1,3) (3,1,1,2)
(1,3,3,2) (2,2,3,1) (3,2,1,1)
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