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 A054963 #13 Jul 24 2022 12:18:15 %S A054963 1,3,9,26,72,194,515,1357,3563,9340,24466,64068,167749,439191,1149837, %T A054963 3010334,7881180,20633222,54018503,141422305,370248431,969323008, %U A054963 2537720614,6643838856,17393795977,45537549099,119218851345 %N A054963 Number of cells in the first column of all directed column-convex polyominoes of area n+1. %H A054963 E. Barcucci, R. Pinzani and R. Sprugnoli, <a href="http://dx.doi.org/10.1007/3-540-56610-4_71">Directed column-convex polyominoes by recurrence relations</a>, Lecture Notes in Computer Science, No. 668, Springer, Berlin (1993), pp. 282-298. %H A054963 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (5,-8,5,-1). %F A054963 a(n) = Fibonacci(2*n) + Fibonacci(2*n+2) - n = A002878(n)-n. %F A054963 G.f.: (1-2x+2x^2)/((1-x)^2(1-3x+x^2)). %F A054963 a(n) = 5*a(n-1) - 8*a(n-2) + 5*a(n-3) - a(n-4) for n >= 4. - _Jinyuan Wang_, Mar 10 2020 %o A054963 (PARI) Vec((1-2*x+2*x^2)/((1-x)^2*(1-3*x+x^2)) + O(x^40)) \\ _Michel Marcus_, Feb 14 2016 %Y A054963 Cf. A000045. %K A054963 nonn %O A054963 0,2 %A A054963 _Emeric Deutsch_, Jun 16 2001