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 A221859 #18 Apr 02 2024 11:39:17 %S A221859 1,4,15,56,209,779,2898,10760,39882,147612,545721,2015721,7440251, %T A221859 27448008,101217076,373128151,1375167467,5067236766,18669118971, %U A221859 68774597447,253334948791,933111590565,3436767111783,12657552835178,46616152422035,171677402416052 %N A221859 Expansion of (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5). %C A221859 A diagonal of the square array A223968. %H A221859 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (9,-28,35,-15,1). %F A221859 a(n) = A223968(n,n+2). %F A221859 G.f.: (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5). %F A221859 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) = 4, a(2) = 15, a(3) = 56, a(4) = 209. %Y A221859 Cf. A223968 %K A221859 nonn,easy %O A221859 0,2 %A A221859 _Philippe Deléham_, Apr 10 2013