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A071706
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Number of complete mappings f(x) of the cyclic group Z_{2n+1} such that -f(-x)=f.
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2
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1, 1, 3, 5, 21, 69, 319, 1957, 12513, 85445, 656771, 5591277, 51531405, 509874417, 5438826975, 62000480093, 752464463029, 9685138399785, 131777883431119
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| A complete mapping of a cyclic group (Zn,+) is a permutation f(x) of Zn such that f(0)=0 and that f(x)-x is also a permutation.
a(n) is the number of complete mappings fixed under rotation R180 where R180(f)(x)=-f(-x). This sequence (n) equals TSQ_R180(n), the number of solutions of the toroidal n-queen problem fixed under rotation R180. A solution of toroidal-semi n-queen problem is a permutation f(x) of Zn such that f(x)-x is also a permutation.
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REFERENCES
| Y. P. Shieh, "Partition strategies for #P-complete problems with applications to enumerative combinatorics", PhD thesis, National Taiwan University, 2001.
Y. P. Shieh, J. Hsiang and D. F. Hsu, "On the enumeration of Abelian k-complete mappings", vol. 144 of Congressus Numerantium, 2000, pp. 67-88.
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LINKS
| Y. P. Shieh, Cyclic complete mappings counting problems
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EXAMPLE
| f(x)=6x in (Z7,+) is a complete mapping of Z7 since that f(0)=0 and that f(x)-x (=5x) is also a permutation of Z7. R180(f)(x)=-f(-x) (=6x). So f(x) is fixed under R180.
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CROSSREFS
| Sequence in context: A110026 A153862 A056803 * A196418 A189560 A179265
Adjacent sequences: A071703 A071704 A071705 * A071707 A071708 A071709
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KEYWORD
| nonn
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AUTHOR
| J. Hsiang, D. F. Hsu and Y. P. Shieh (arping(AT)turing.csie.ntu.edu.tw), Jun 03 2002
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