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%I
%S 1,12,36,100,233,456,796,1280,1935,2788,3866,5196,6805,8720,10968,
%T 13576,16571,19980,23830,28148,32961,38296,44180,50640,57703
%N Number of ways to place 3 nonattacking knights on a 3 X n board
%H V. Kotesovec, <a href="http://web.telecom.cz/vaclav.kotesovec/math.htm">Number of ways of placing non-attacking queens and kings on boards of various sizes</a>
%F Explicit formula (Vaclav Kotesovec, 26.1.2010): a(n) = (9n^3-45n^2+122n-144)/2, n>=4
%F G.f.: x*(6*x^6-8*x^5+2*x^4+24*x^3-6*x^2+8*x+1)/(x-1)^4 [From _Vaclav Kotesovec_, Mar 25 2010]
%Y A172134, A061989, A047659, A172202
%K nonn
%O 1,2
%A _Vaclav Kotesovec_, Jan 29 2010
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