Atkinson, M. D. Permutations which are the union of an increasing and a decreasing subsequence. (English) Zbl 0885.05011 Electron. J. Comb. 5, Research paper R6, 13 p. (1998); printed version J. Comb. 5, 87-99 (1998). Summary: It is shown that there are \({2n\choose n}-\sum_{m=0}^{n-1}2^{n-m-1}{2m\choose m}\) permutations which are the union of an increasing sequence and a decreasing sequence. Cited in 13 Documents MSC: 05A15 Exact enumeration problems, generating functions Keywords:permutations; sequences PDFBibTeX XMLCite \textit{M. D. Atkinson}, Electron. J. Comb. 5, No. 1, Research paper R6, 13 p. (1998; Zbl 0885.05011) Full Text: EuDML EMIS Online Encyclopedia of Integer Sequences: Number of permutations which are the union of an increasing and a decreasing subsequence.