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 A172212 Number of ways to place 3 nonattacking knights on a 3 X n board. 7
 1, 12, 36, 100, 233, 456, 796, 1280, 1935, 2788, 3866, 5196, 6805, 8720, 10968, 13576, 16571, 19980, 23830, 28148, 32961, 38296, 44180, 50640, 57703, 65396, 73746, 82780, 92525, 103008, 114256, 126296, 139155, 152860, 167438, 182916, 199321 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = (9n^3 - 45n^2 + 122n - 144)/2, n>=4. G.f.: x*(6*x^6-8*x^5+2*x^4+24*x^3-6*x^2+8*x+1)/(x-1)^4. - Vaclav Kotesovec, Mar 25 2010 MATHEMATICA CoefficientList[Series[(6 x^6 - 8 x^5 + 2 x^4 + 24 x^3 - 6 x^2 + 8 x + 1) / (x - 1)^4, {x, 0, 50}], x] (* Vincenzo Librandi, May 27 2013 *) CROSSREFS Cf. A172134, A061989, A047659, A172202. Sequence in context: A212963 A033196 A172218 * A060621 A058880 A282097 Adjacent sequences:  A172209 A172210 A172211 * A172213 A172214 A172215 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Jan 29 2010 STATUS approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)