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 A224422 #15 Feb 16 2024 12:33:44
%S A224422 1,5,20,75,275,1001,3639,13243,48280,176341,645150,2363596,8669142,
%T A224422 31825005,116914020,429737220,1580244061,5812839156,21387636101,
%U A224422 78708626396,289699273501,1066406842677,3925882147566,14453780545834,53216783798234,195944670698910
%N A224422 Expansion of (1-x)*(1-3*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).
%C A224422 A diagonal of the square array A223968.
%H A224422 Michael De Vlieger, <a href="/A224422/b224422.txt">Table of n, a(n) for n = 0..1766</a>
%H A224422 László Németh and László Szalay, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL24/Nemeth/nemeth8.html">Sequences Involving Square Zig-Zag Shapes</a>, J. Int. Seq., Vol. 24 (2021), Article 21.5.2.
%H A224422 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (9,-28,35,-15,1).
%F A224422 a(n) = A223968(n+3,n) = A223968(n+4,n).
%F A224422 a(n) = 9*a(n-1) - 28*a(n-2) + 35*a(n-3) - 15*a(n-4) + a(n-5) with a(0) = 1, a(1) = 5, a(2) = 20, a(3) = 75, a(4) = 275.
%t A224422 LinearRecurrence[{9, -28, 35, -15, 1}, {1, 5, 20, 75, 275}, 26] (* _Michael De Vlieger_, Aug 05 2021 *)
%Y A224422 Cf. A223968.
%K A224422 nonn,easy
%O A224422 0,2
%A A224422 _Philippe Deléham_, Apr 06 2013