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 A193768 #28 Jan 19 2022 17:25:34
%S A193768 2,3,4,4,6,7,7,8,10,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,
%T A193768 26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,
%U A193768 49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67
%N A193768 The domination number of the 4 X n board.
%C A193768 The domination number of a rectangular grid is the minimal number of X-pentominoes or its fragments that can cover the board.
%H A193768 Andrew Buchanan, Tanya Khovanova and Alex Ryba, <a href="http://arxiv.org/abs/1112.2115">Saturated Domino Coverings</a>, arXiv:1112.2115 [math.CO], 2011.
%H A193768 M. S. Jacobson and L. F. Kinch, <a href="http://www.math.ucdenver.edu/~msj/papers/DomProdI.pdf">On the domination number of products of graphs:I</a>, Ars Combinatoria, vol 18, 1983, 33-44.
%H A193768 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A193768 a(n) = n, except for n = 1, 2, 3, 5, 6 or 9. For the exceptions a(n) = n+1.
%F A193768 a(n) = 4n - A193767(n).
%F A193768 a(n) = 2*a(n-1)-a(n-2) for n>11. - _Colin Barker_, Oct 05 2014
%F A193768 G.f.: x*(x^10-2*x^9+x^8+x^7-x^6-x^5+2*x^4-x^3-x+2) / (x-1)^2. - _Colin Barker_, Oct 05 2014
%e A193768 You can't cover the 1 by 4 board with an X-pentomino, but you can do it with two of them.
%t A193768 LinearRecurrence[{2,-1},{2,3,4,4,6,7,7,8,10,10,11},70] (* _Harvey P. Dale_, Feb 17 2020 *)
%o A193768 (PARI) Vec(x*(x^10-2*x^9+x^8+x^7-x^6-x^5+2*x^4-x^3-x+2)/(x-1)^2 + O(x^100)) \\ _Colin Barker_, Oct 05 2014
%Y A193768 Row 4 of A350823.
%Y A193768 Cf. A193764, A193765, A193766, A193767.
%K A193768 nonn,easy
%O A193768 1,1
%A A193768 Andrew Buchanan, _Tanya Khovanova_, Alex Ryba, Aug 06 2011