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A230554
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Number of involutions avoiding the pattern 1324.
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0
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1, 1, 2, 4, 9, 21, 51, 126, 321, 820, 2160, 5654, 15272, 40758, 112280, 304471, 852164, 2341980, 6640755, 18460066, 52915999
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OFFSET
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0,3
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LINKS
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EXAMPLE
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Of the 26 involutions of length 5, only 21435, 13254, 13245, 14325, and 12435 contain the pattern 1324, so a(5) = 21.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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