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 A224514 #20 Apr 02 2024 11:39:04
%S A224514 1,2,6,20,70,251,911,3327,12190,44744,164407,604487,2223504,8181175,
%T A224514 30108147,110820165,407946421,1501844193,5529362694,20358557249,
%U A224514 74961030414,276017648570,1016360893036,3742540945813,13781324308298,50748099850042
%N A224514 Expansion of (1-x)*(1-3*x)*(1-3*x+x^2)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).
%C A224514 A diagonal of the square array A223968.
%H A224514 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (9,-28,35,-15,1).
%F A224514 a(n) = A223968(n,n).
%F A224514 G.f.: (1-x)*(1-3*x)*(1-3*x+x^2)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).
%F A224514 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) = 2, a(2) = 6, a(3) = 20, a(4) = 70.
%t A224514 LinearRecurrence[{9,-28,35,-15,1},{1,2,6,20,70,251,911,3327,12190,44744,164407,604487,2223504,8181175},40] (* _Harvey P. Dale_, Apr 24 2016 *)
%Y A224514 Cf. A223968
%K A224514 nonn,easy
%O A224514 0,2
%A A224514 _Philippe Deléham_, Apr 08 2013
%E A224514 a(8) corrected by _Georg Fischer_, May 10 2019