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 A217782 #13 Oct 02 2023 13:49:07 %S A217782 1,2,6,20,69,242,857,3054,10930,39236,141153,508598,1834641,6623450, %T A217782 23926334,86468052,312587197,1130277914,4087621545,14784539846, %U A217782 53478888618,193456813508,699850536281,2531866279710,9159810802849,33139021206962,119894215708662 %N A217782 Expansion of (1-x)*(1-2x)*(1-3x)/((1-5x+5*x^2)*(1-3x+x^2)). %C A217782 A diagonal of the square array A217770. %H A217782 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (8, -21, 20, -5). %F A217782 a(n) = A217770(n,n). %F A217782 a(n) = 8*a(n-1) - 21*a(n-2) + 20*a(n-3) -5*a(n-4) for n>=4, a(0) = 1, a(1) = 2, a(2) = 6, a(3) = 20. %Y A217782 Cf. A217770, A217777, A217778, A217779. %K A217782 nonn,easy %O A217782 0,2 %A A217782 _Philippe Deléham_, Mar 24 2013