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 A172138 Number of ways to place 3 nonattacking zebras on an n X n board. 6
 0, 4, 84, 452, 1772, 5596, 14888, 34640, 72712, 140716, 255036, 437968, 718980, 1136092, 1737376, 2582576, 3744848, 5312620, 7391572, 10106736, 13604716, 18056028, 23657560, 30635152, 39246296, 49782956, 62574508, 77990800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Zebra is a (fairy chess) leaper [2,3]. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = (n^6 - 27n^4 + 120n^3 + 74n^2 - 1608n + 2976)/6, n >=6. G.f.: 4*x^2*(4*x^10-23*x^9+45*x^8-33*x^7-x^6+9*x^5+29*x^4-58*x^3+13*x^2-14*x-1)/(x-1)^7. - Vaclav Kotesovec, Mar 25 2010 MATHEMATICA CoefficientList[Series[4 x (4 x^10 - 23 x^9 + 45 x^8 - 33 x^7 - x^6 + 9 x^5 + 29 x^4 - 58 x^3 + 13 x^2 - 14 x - 1) / (x - 1)^7, {x, 0, 40}], x] (* Vincenzo Librandi, May 27 2013 *) CROSSREFS Cf. A047659, A172124, A172134, A172137. Sequence in context: A316490 A102982 A231741 * A282588 A178208 A069441 Adjacent sequences:  A172135 A172136 A172137 * A172139 A172140 A172141 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Jan 26 2010 STATUS approved

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Last modified September 22 01:42 EDT 2020. Contains 337276 sequences. (Running on oeis4.)