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

# Toufik Mansour and Julian West

#
Avoiding 2-letter Signed Patterns

**Abstract.**
Let *B*_{n} be the hyperoctahedral group, the set of all signed
permutations on *n* letters, and let *B*_{n}(*T*)
be the set of all
signed permutations in *B*_{n} which avoid a set *T* of signed
patterns. In this paper, we find all the cardinalities of the sets
*B*_{n}(*T*) where *T \subseteq B*_{2}.
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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