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A172964
Number of ways to place 2 nonattacking knights on an n X n cylindrical board.
5
0, 4, 18, 92, 230, 522, 1022, 1808, 2970, 4610, 6842, 9792, 13598, 18410, 24390, 31712, 40562, 51138, 63650, 78320, 95382, 115082, 137678, 163440, 192650, 225602, 262602, 303968, 350030, 401130, 457622, 519872, 588258, 663170, 745010, 834192, 931142, 1036298, 1150110
OFFSET
1,2
FORMULA
a(n) = n*(n^3 - 9*n + 12)/2, n>=5.
G.f.: 2*x^2*(6*x^7-30*x^6+61*x^5-66*x^4+45*x^3-21*x^2+x-2)/(x-1)^5. - Vaclav Kotesovec, Mar 25 2010
MATHEMATICA
CoefficientList[Series[2 x (6 x^7 - 30 x^6 + 61 x^5 - 66 x^4 + 45 * x^3 - 21 x^2 + x - 2) / (x - 1)^5, {x, 0, 50}], x] (* Vincenzo Librandi, May 29 2013 *)
CROSSREFS
Sequence in context: A269450 A206639 A367875 * A317135 A196150 A185298
KEYWORD
nonn,easy
AUTHOR
Vaclav Kotesovec, Feb 06 2010
EXTENSIONS
More terms from Vincenzo Librandi, May 29 2013
STATUS
approved