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 A172221 Number of ways to place 3 nonattacking zebras on a 3 X n board. 4
 1, 20, 84, 200, 403, 720, 1180, 1808, 2631, 3676, 4970, 6540, 8413, 10616, 13176, 16120, 19475, 23268, 27526, 32276, 37545, 43360, 49748, 56736, 64351, 72620, 81570, 91228, 101621, 112776, 124720, 137480, 151083, 165556, 180926, 197220 (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 Eric Weisstein's World of Mathematics, Zebra Graph Wikipedia, Zebra (chess) FORMULA a(n) = (9*n^3 - 21*n^2 + 50*n - 48)/2, n>=6. G.f.: x*(2*x^8-4*x^7+2*x^6-8*x^5+28*x^4-20*x^3+10*x^2+16*x+1)/(x-1)^4. - Vaclav Kotesovec, Mar 25 2010 MATHEMATICA CoefficientList[Series[(2 x^8 - 4 x^7 + 2 x^6 - 8 x^5 + 28 x^4 - 20 x^3 + 10 x^2 + 16 x + 1) / (x - 1)^4, {x, 0, 50}], x] (* Vincenzo Librandi, May 28 2013 *) CROSSREFS Cf. A172138, A061989. Sequence in context: A156389 A044207 A044588 * A006566 A205312 A268888 Adjacent sequences:  A172218 A172219 A172220 * A172222 A172223 A172224 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Jan 29 2010 EXTENSIONS More terms from Vincenzo Librandi, May 28 2013 STATUS approved

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Last modified December 18 20:06 EST 2018. Contains 318245 sequences. (Running on oeis4.)