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Search: id:A129815
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| A129815 |
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Number of reverse alternating fixed-point-free permutations on n letters. |
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+0
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
(list; graph; listen)
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OFFSET
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1,4
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COMMENT
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Contribution from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 06 2009: (Start)
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.
a(2n-1)=A129817(2n-1)
(End)
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LINKS
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R. P. Stanley, Alternating permutations and symmetric functions
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EXAMPLE
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Contribution from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 06 2009: (Start)
a(4)=2 because we have 3412 and 2413.
(End)
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CROSSREFS
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Cf. A000111, A000166, A007779.
Sequence in context: A002772 A000140 A079263 this_sequence A103941 A064643 A129535
Adjacent sequences: A129812 A129813 A129814 this_sequence A129816 A129817 A129818
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KEYWORD
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more,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)eunet.rs), May 20 2007
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