%I #12 Jan 29 2023 17:21:36
%S 1,5,431,555195,10286937043,2692324030864335,9852929684161379901975,
%T 501079193080617800221189943995,
%U 352690403996687922642590703716802346343,3426297680513758764075706102615040790667832304415,458508006189588425325361635000918336126387961057365005349963
%N Number of connected spanning subgraphs in the n X n grid graph.
%C For n > 1, a(n) is the number of connected edge covers in the n X n grid graph.
%H Andrew Howroyd, <a href="/A359992/b359992.txt">Table of n, a(n) for n = 1..15</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/GridGraph.html">Grid Graph</a>
%F a(n) = A053765(n) - A359989(n).
%e The a(2) = 5 connected spanning subgraphs are the following subgraphs and their rotations and reflections.
%e o---o o---o
%e | | |
%e o---o o---o
%Y Main diagonal of A359993.
%Y Cf. A007341, A053765, A080691, A286913, A359989.
%K nonn
%O 1,2
%A _Andrew Howroyd_, Jan 28 2023