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A243464
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Number of ways 2 domicules can be placed on an n X n square.
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2
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0, 0, 3, 110, 657, 2172, 5375, 11178, 20685, 35192, 56187, 85350, 124553, 175860, 241527, 324002, 425925, 550128, 699635, 877662, 1087617, 1333100, 1617903, 1946010, 2321597, 2749032, 3232875, 3777878, 4388985, 5071332, 5830247, 6671250, 7600053, 8622560
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f.: x^2*(43*x^3-137*x^2-95*x-3)/(x-1)^5.
a(n) = -43+63*n-4*n^2-24*n^3+8*n^4 for n>0, a(0) = 0.
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EXAMPLE
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a(2) = 3:
+---+ +---+ +---+
|o-o| |o o| |o o|
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|o-o| |o o| |o o|
+---+ +---+ +---+.
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MAPLE
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a:= n-> `if`(n=0, 0, (((8*n-24)*n-4)*n+63)*n-43):
seq(a(n), n=0..50);
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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