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 A375817 #16 Sep 04 2024 08:47:49 %S A375817 1,4,56,1112,25000,607712,15918280,451371888,13908978792,466254401360, %T A375817 16972978214456,668532916285104,28362769354991656,1290007395847848160, %U A375817 62619708755213093360,3230982278203826268640,176553522584025285715304,10184062836771923067636528 %N A375817 In an n X n grid draw straight walls between cells, starting at a border, such that the resulting figure is connected and has only one-cell wide paths; a(n) is the number of solutions not reduced for symmetries. %C A375817 This sequence contains some, but not all of the spanning trees in A007341, a(n)<A007341(n), for n>2. %C A375817 See A375770 for examples. %H A375817 Andrew Howroyd, <a href="/A375817/b375817.txt">Table of n, a(n) for n = 1..100</a> %e A375817 a(3) = 56. The A375770(3) = 10 distinct solutions with their multiplicities are: %e A375817 ._._._. ._._._. ._._._. ._._._. ._._._. %e A375817 | | | | | | | | | | | | | ._| %e A375817 | | | | | | | | | | | | | | | | %e A375817 |_|_|_| |_|_|_| |_|_._| |_|_|_| |_|_|_| %e A375817 (4) (8) (4) (2) (8) %e A375817 ._._._. ._._._. ._._._. ._._._. ._._._. %e A375817 | | ._| | | | | ._| |_. ._| |_. | | %e A375817 | | | | ._| | | ._| | | | ._| %e A375817 |_|_|_| |_|_._| |_|_._| |_|_|_| |_|_._| %e A375817 (8) (8) (8) (4) (2) %o A375817 (PARI) \\ See PARI link in A375770 for program code. %o A375817 vector(20, n, A375817(n)) \\ _Andrew Howroyd_, Sep 03 2024 %Y A375817 Main diagonal of A375858. %Y A375817 Cf. A007341, A375770 (up to rotations and reflections), A375859 (up to rotations), A375860 (up to symmetries of the rectangle). %K A375817 nonn %O A375817 1,2 %A A375817 _Lars Blomberg_, Aug 30 2024 %E A375817 Terms corrected and extended by _Andrew Howroyd_, Sep 03 2024