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arxiv: math/0210058 · v1 · submitted 2002-10-04 · 🧮 math.CO

Restricted 132-alternating permutations and Chebyshev polynomials

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keywords alternatingavoidchebyshevcontainexactlyfunctiongeneratingletters
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A permutation is said to be \emph{alternating} if it starts with rise and then descents and rises come in turn. In this paper we study the generating function for the number of alternating permutations on $n$ letters that avoid or contain exactly once 132 and also avoid or contain exactly once an arbitrary pattern on $k$ letters. In several interesting cases the generating function depends only on $k$ and is expressed via Chebyshev polynomials of the second kind.

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