This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A359992 #13 Feb 16 2025 08:34:04 %S A359992 1,5,431,555195,10286937043,2692324030864335,9852929684161379901975, %T A359992 501079193080617800221189943995, %U A359992 352690403996687922642590703716802346343,3426297680513758764075706102615040790667832304415,458508006189588425325361635000918336126387961057365005349963 %N A359992 Number of connected spanning subgraphs in the n X n grid graph. %C A359992 For n > 1, a(n) is the number of connected edge covers in the n X n grid graph. %H A359992 Andrew Howroyd, <a href="/A359992/b359992.txt">Table of n, a(n) for n = 1..15</a> %H A359992 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GridGraph.html">Grid Graph</a> %F A359992 a(n) = A053765(n) - A359989(n). %e A359992 The a(2) = 5 connected spanning subgraphs are the following subgraphs and their rotations and reflections. %e A359992 o---o o---o %e A359992 | | | %e A359992 o---o o---o %Y A359992 Main diagonal of A359993. %Y A359992 Cf. A007341, A053765, A080691, A286913, A359989. %K A359992 nonn %O A359992 1,2 %A A359992 _Andrew Howroyd_, Jan 28 2023