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 A071706 Number of complete mappings f(x) of the cyclic group Z_{2n+1} such that -f(-x)=f. 2
 1, 1, 3, 5, 21, 69, 319, 1957, 12513, 85445, 656771, 5591277, 51531405, 509874417, 5438826975, 62000480093, 752464463029, 9685138399785, 131777883431119 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 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. 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. LINKS Y. P. Shieh, Cyclic complete mappings counting problems 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. CROSSREFS Sequence in context: A264683 A286033 A056803 * A196418 A189560 A216385 Adjacent sequences:  A071703 A071704 A071705 * A071707 A071708 A071709 KEYWORD nonn AUTHOR J. Hsiang, D. F. Hsu and Y. P. Shieh (arping(AT)turing.csie.ntu.edu.tw), Jun 03 2002 STATUS approved

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Last modified February 18 00:19 EST 2019. Contains 320237 sequences. (Running on oeis4.)