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A059525 Number of nonzero n X n binary arrays with all 1's connected. 17
0, 1, 13, 218, 11506, 2301877, 1732082741, 4872949974666, 51016818604894742, 1980555831431088025753, 284374318545830329487309785, 150730745416633777472365437495914, 294516896499779486414143877573183893666, 2119097214294718323017954923662829194285541981 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..16

Eric Weisstein's World of Mathematics, Connected Graph

Eric Weisstein's World of Mathematics, Grid Graph

Eric Weisstein's World of Mathematics, Induced Subgraph

MATHEMATICA

Table[Count[Subgraph[GridGraph[{n, n}], #] & /@ Subsets[Range[n^2], {1, Infinity}], _?ConnectedGraphQ], {n, 4}] (* Eric W. Weisstein, May 01 2017 *)

CROSSREFS

Main diagonal of A287151.

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).

Sequence in context: A218475 A294982 A320627 * A086147 A015253 A051621

Adjacent sequences:  A059522 A059523 A059524 * A059526 A059527 A059528

KEYWORD

nonn,hard

AUTHOR

David Radcliffe, Jan 21 2001

EXTENSIONS

One more term from John W. Layman, Jan 25 2001

More terms from R. H. Hardin, Feb 28 2002

Clearer name from R. H. Hardin, Jul 06 2009

a(8)-a(9) from Giovanni Resta, May 03 2017

a(10)-a(13) from Andrew Howroyd, May 20 2017

STATUS

approved

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Last modified July 18 11:30 EDT 2019. Contains 325138 sequences. (Running on oeis4.)