id:A140789 - OEIS Search Results

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We consider how many ways there are of coloring a square grid, n by n, using just two colors, black & white say. If the resulting grid has TWO lines of symmetry, then the number of different grids is given by this sequence. None of these counted are the images of any of the others under a rotation. If one wishes to count these as different, then each of these numbers can be multiplied by 2.

+0
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0, 1, 8, 32, 448, 2240, 64512, 556032, 33521664, 553615360, 68717379584, 2233380896768 (list; graph; listen)

	OFFSET	`1,3`
	FORMULA	`a(2m) = 2^(m^2 - 1)(2^m + 1) - 2^(m(m + 1)/2) for n even a(2m+1)= 2^(m^2 + 2m + 1) - 2^((m^2 + 3m + 2)/2) for n odd`
	CROSSREFS	`Cf. A140650.` `Sequence in context: A143557 A034193 A159277 this_sequence A120781 A139286 A139306` `Adjacent sequences: A140786 A140787 A140788 this_sequence A140790 A140791 A140792`
	KEYWORD	`nonn`
	AUTHOR	`Anthony C Robin (anthony_robin(AT)hotmail.com), Jul 14 2008`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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