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A047937
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Number of 2-colorings of an n X n grid, up to rotational symmetry.
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15
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1, 2, 6, 140, 16456, 8390720, 17179934976, 140737496748032, 4611686019501162496, 604462909807864344215552, 316912650057057631849169289216, 664613997892457937028364283517337600, 5575186299632655785385110159782842147536896, 187072209578355573530071668259090783437390809661440
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OFFSET
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0,2
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COMMENTS
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Cycle index = 1/4(s_1^(n^2)+ 2 s_4^floor(n^2/4)s_1^(n mod 2)+s_2^floor(n^2/2)s_1^(n mod 2)). - Geoffrey Critzer, Oct 28 2011
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LINKS
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FORMULA
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a(n) = (m^(n^2) + 2*m^((n^2 + 3*(n mod 2))/4) + m^((n^2 + (n mod 2))/2))/4, with m = 2.
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EXAMPLE
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a(2)=6 from
00 10 11 10 11 11
00 00 00 01 10 11
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MATHEMATICA
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Table[(2^(n^2)+2*2^Floor[n^2/4]*2^Mod[n, 2]+2^Floor[n^2/2]*2^Mod[n, 2])/4, {n, 0, 10}] (* Geoffrey Critzer, Oct 28 2011 *)
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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