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A020877
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Number of matchings in Moebius ladder M_n.
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0
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10, 34, 106, 344, 1102, 3546, 11394, 36628, 117730, 378426, 1216378, 3909832, 12567446, 40395794, 129844994, 417363332, 1341539194, 4312135922, 13860583626, 44552347608, 143205490526, 460308235562, 1479577849602
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| Also the Hosoya indices of the Moebius ladders - Eric Weisstein, Jul 11 2011.
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REFERENCES
| J. P. McSorley, Counting structures in the Moebius ladder, Discrete Math., 184 (1998), 137-164.
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LINKS
| Eric Weisstein's World of Mathematics, Hosoya Index
Eric Weisstein's World of Mathematics, Moebius Ladder
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FORMULA
| G.f.=2x^2*(5+7x-x^2-2x^3)/[(1+x)(1-3x-x^2+x^3)]. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 21 2004
The McSorley reference gives the approximation a(n)~(3.2143)^n+(-0.6751)^n+(0.4608)^n-(-1)^n. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 21 2004
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MAPLE
| G:=2*x^2*(5+7*x-x^2-2*x^3)/(1+x)/(1-3*x-x^2+x^3): Gser:=series(G, x=0, 29): seq(coeff(Gser, x^n), n=2..27); (Deutsch)
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CROSSREFS
| Sequence in context: A007584 A009924 A019257 * A119171 A119229 A119227
Adjacent sequences: A020874 A020875 A020876 * A020878 A020879 A020880
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 21 2004
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