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 A209798 The number of partitions of the set [n] where each element can be colored 1 or 2 avoiding the patterns 1^11^2, 1^12^2, and 1^22^1 in the pattern sense. 0
 2, 5, 12, 33, 108, 411, 1760, 8287, 42302, 231959, 1357150, 8427205, 55288886, 381798657, 2765917104, 20960284309, 165729739624, 1364153612335, 11665484410132, 103448316470763, 949739632313522, 9013431476894667, 88304011710168714, 891917738589610601 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A partition of the set [n] is a family nonempty disjoint sets whose union is [n].  The blocks are written in order of increasing minima.  A partition of the set [n] can be written as a word p=p_1p_2...p_n where p_i=j if element i is in block j.  A partition q=q_1q_2...q_n contains partition p=p_1p_2...p_k if there is a subword q_{i_1}q_{i_2}...q_{i_k} such that q_{i_a}

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Last modified June 14 21:27 EDT 2021. Contains 345041 sequences. (Running on oeis4.)