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A133130
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Number of 0/1 colorings of an n X n square for which no 2 by 2 subsquare is monochromatic.
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1
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OFFSET
| 1,1
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COMMENTS
| For each n we define an undirected labeled graph (with self loops), where the vertices are labeled with strings from {0,1}^n and there is an edge between two vertices exactly when we can form a 2 X n rectangle whose rows are the two labels and the 2 X n rectangle has no monochromatic 2 X 2 subsquares. a(n) is the number of walks of length n in this graph. Thus it is the sum of all of the entries of A^n, where A is the adjacency matrix of the graph.
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EXAMPLE
| a(2) = 14 because 2 of the 16 colorings are monochromatic
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CROSSREFS
| Cf. A055099.
Sequence in context: A205619 A034912 A035018 * A090598 A060075 A035273
Adjacent sequences: A133127 A133128 A133129 * A133131 A133132 A133133
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KEYWORD
| nonn
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AUTHOR
| Victor S. MIller (victor(AT)idaccr.org), Sep 19 2007
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