On pattern avoiding flattened set partitions |
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Authors: | Thomas Y H Liu Andy Q Zhang |
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Institution: | 1. Department of Foundation Courses, Southwest Jiaotong University, Emeishan, Sichuan 614202, P. R. China;
2. Center for Combinatorics, LPMC-TJKLC, Nankai University, Tianjin 300071, P. R. China |
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Abstract: | Let Π = B1/B2/…/Bk be any set partition of n] = {1, 2,…, n} satisfying that entries are increasing in each block and blocks are arranged in increasing order of their first entries. Then Callan defined the flattened Π to be the permutation of n] obtained by erasing the divers between its blocks, and Callan also enumerated the number of set partitions of n] whose flattening avoids a single 3-letter pattern. Mansour posed the question of counting set partitions of n] whose flattening avoids a pattern of length 4. In this paper, we present the number of set partitions of n] whose flattening avoids one of the patterns: 1234, 1243, 1324, 1342, 1423, 1432, 3142 and 4132. |
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Keywords: | Set partition pattern avoidance flattened partition |
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