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A305785
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Number of set partitions of [n] with alternating parity of elements and exactly ceiling(n/2) blocks.
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1
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1, 1, 1, 2, 3, 7, 14, 33, 84, 204, 627, 1558, 5692, 14402, 60752, 155828, 747046, 1937292, 10385051, 27176489, 161160411, 424958631, 2760858706, 7327447983, 51762453941, 138150105263, 1054164297384, 2827224795106, 23174732414244, 62420125297576, 546984814641114
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OFFSET
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0,4
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LINKS
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FORMULA
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EXAMPLE
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a(5) = 7: 123|4|5, 12|34|5, 12|3|45, 1|234|5, 145|2|3, 1|2|345, 1|23|45.
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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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