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A059525
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Number of nonzero n X n binary arrays with all 1's connected.
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23
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0, 1, 13, 218, 11506, 2301877, 1732082741, 4872949974666, 51016818604894742, 1980555831431088025753, 284374318545830329487309785, 150730745416633777472365437495914, 294516896499779486414143877573183893666, 2119097214294718323017954923662829194285541981
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OFFSET
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0,3
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COMMENTS
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Old name was: "Number of n X n checkerboards in which the set of red squares is edge connected".
Also the number of connected induced (non-null) subgraphs of the n X n grid graph P_n x P_n. - Eric W. Weisstein, May 01 2017
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LINKS
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MATHEMATICA
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Table[Count[Subgraph[GridGraph[{n, n}], #] & /@ Subsets[Range[n^2], {1, Infinity}], _?ConnectedGraphQ], {n, 4}] (* Eric W. Weisstein, May 01 2017 *)
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CROSSREFS
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Cf. A059021, A020873 (wheel), A059020 (ladder), A286139 (king), A286182 (prism), A286183 (antiprism), A286184 (helm), A286185 (Möbius ladder), A286186 (friendship), A286187 (web), A286188 (gear), A286189 (rook), A285765 (queen).
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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