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A129815
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Number of reverse alternating fixed-point-free permutations on n letters.
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4
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0, 0, 1, 2, 6, 22, 102, 506, 2952, 18502, 131112, 991226, 8271792, 73176262, 703077552, 7121578106, 77437418112, 883521487942, 10726837356672, 136104948161786, 1825110309733632
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OFFSET
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1,4
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COMMENTS
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Reverse alternating permutations are called also up-down permutations.
a(n) is also the number of reverse alternating permutations having exactly 1 fixed point (see the Stanley reference). Example: a(4)=2 because we have 1423 and 2314.
(End)
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LINKS
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FORMULA
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EXAMPLE
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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