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 A061534 #22 Jul 11 2023 15:18:49 %S A061534 1,3,9,29,93,299,961,3089,9929,31915,102585,329741,1059893,3406835, %T A061534 10950657,35198913,113140561,363669939,1168951465,3757383773, %U A061534 12077432845,38820730843,124782241601,401090022801,1289231579161,4144002518683,13320149112409 %N A061534 Expansion of (1-x^2)/(1-3*x-x^2+x^3). %C A061534 The number of tilings of a 2*n grid using dominoes and singletons with two horizontal dominoes or one vertical domino in the two rightmost squares. - _John M. Campbell_, Mar 05 2011 %H A061534 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=1056">Encyclopedia of Combinatorial Structures 1056</a> %H A061534 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,1,-1). %F A061534 a(n) = 3*a(n-1)+a(n-2)-a(n-3) for n>3. - _Colin Barker_, Sep 13 2014 %F A061534 G.f.: -(x-1)*(x+1) / (x^3-x^2-3*x+1). - _Colin Barker_, Sep 13 2014 %F A061534 a(n) = A033505(n)-A033505(n-2). - _R. J. Mathar_, Oct 24 2015 %o A061534 (PARI) Vec(-(x-1)*(x+1)/(x^3-x^2-3*x+1) + O(x^100)) \\ _Colin Barker_, Sep 13 2014 %Y A061534 Cf. A033505. %K A061534 nonn,easy %O A061534 0,2 %A A061534 _Henry Bottomley_, May 16 2001