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Search: id:A075866
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| A075866 |
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Number of permutations s of {1,2,...,n} such that |s(i)-i| for i=1,2,...,n are all distinct. |
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+0
2
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| 1, 0, 0, 4, 4, 0, 0, 32, 96, 0, 0, 992, 2512, 0, 0, 50512, 144144, 0, 0, 3717888, 11068560, 0, 0, 378849504, 1269763552, 0, 0, 51487458416, 181839037824, 0, 0
(list; graph; listen)
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OFFSET
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1,4
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COMMENT
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a(n)=0 iff n=2,3 mod 4
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REFERENCES
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H. A. Shah Ali, Problem 10964, Amer. Math. Monthly, 109 (2002), 759.
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EXAMPLE
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a(8)=32, since the following 32 permutations of {12345678} and no others, have the required property:
(87265314)(87361542)(87362514)(87364215)(87514632)(87531642)(87532614)
(87541362)(83765142)(85724613)(84752613)(85743162)(86275413)(86374152)
(86357142)(86542713)(48753621)(68275431)(68374251)(58376421)(58473621)
(68357241)(68542731)(58643721)(73865241)(75824631)(74852631)(75843261)
(73685421)(75386421)(75483621)(76358421)
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CROSSREFS
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Sequence in context: A098445 A143266 A133845 this_sequence A156450 A067007 A066298
Adjacent sequences: A075863 A075864 A075865 this_sequence A075867 A075868 A075869
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KEYWORD
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more,nonn
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AUTHOR
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Reiner Martin (reinermartin(AT)hotmail.com), Oct 15 2002
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EXTENSIONS
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Extended and edited by John W. Layman (layman(AT)math.vt.edu), Oct 05 2004
a(17)-a(27) from Al Zimmermann (alzimmerma(AT)aol.com), Aug 03 2007
a(28) through a(31) from Al Zimmermann (alzimmerma(AT)aol.com), Aug 22 2007
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