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 A060521 #9 Oct 14 2024 12:17:32 %S A060521 6,36,102,378,1260,4374,14946,51384,176238,605022,2076288,7126302, %T A060521 24457806,83942100,288096942,988778082,3393583068,11647114446, %U A060521 39974047290,137194888728,470866430838,1616060190870,5546478488640 %N A060521 Number of 3 X n grids of black and white cells, no 3 of same color vertically or horizontally contiguous. %C A060521 The conjectured recursion is correct: For each n count the solutions separately where the last two rows differ in 0, 1, 2, or 3 places; a linear recursion is then readily found. The corresponding matrix has characteristic polynomial x^4 - 2 x^3 - 5 x^2 + 1, matching the recursion recursion a(n+4) = 2a(n+3) + 5a(n+2) - a(n). [From _Hagen von Eitzen_, Oct 21 2009] %H A060521 Robert Dougherty-Bliss, Christoph Koutschan, Natalya Ter-Saakov, and Doron Zeilberger, <a href="https://arxiv.org/abs/2410.07435">The (Symbolic and Numeric) Computational Challenges of Counting 0-1 Balanced Matrices</a>, arXiv:2410.07435 [math.CO], 2024. See p. 6. %F A060521 Almost surely satisfies a(n+4) = 2a(n+3) + 5a(n+2) - a(n). %K A060521 nonn %O A060521 1,1 %A A060521 Tom Womack (tom(AT)womack.net) %E A060521 More terms from _Hagen von Eitzen_, Oct 21 2009