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Abstract : |
Abstract. Up?down permutations are counted by tangent resp. secant numbers. Considering words instead, where the letters are produced by independent geometric distributions, there are several ways of introducing this concept; in the limit they all coincide with the classical version. In this way, we get some new q?tangent and q?secant functions. Some of them also have nice continued fraction expansions; in one particular case, we could not find a proof for it. Divisibility results la Andrews/Foata/Gessel are also discussed. 1., |
