Séminaire Lotharingien de Combinatoire, B49a (2002), 11 pp.

Toufik Mansour and Julian West

Avoiding 2-letter Signed Patterns

Abstract. Let Bn be the hyperoctahedral group, the set of all signed permutations on n letters, and let Bn(T) be the set of all signed permutations in Bn which avoid a set T of signed patterns. In this paper, we find all the cardinalities of the sets Bn(T) where T \subseteq B2. Some of the cardinalities encountered involve inverse binomial coefficients, binomial coefficients, Catalan numbers, and Fibonacci numbers.

Received: July 25, 2002. Accepted: November 15, 2002. Final version: December 3, 2002.

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