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 A078071 #9 Mar 13 2021 08:06:07 %S A078071 1,-3,4,-4,6,-12,20,-28,40,-64,104,-160,240,-368,576,-896,1376,-2112, %T A078071 3264,-5056,7808,-12032,18560,-28672,44288,-68352,105472,-162816, %U A078071 251392,-388096,599040,-924672,1427456,-2203648,3401728,-5251072,8105984,-12513280,19316736,-29818880,46030848 %N A078071 Expansion of (1-x)/(1+2*x+2*x^2+2*x^3). %H A078071 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-2,-2). %F A078071 a(0) = 1, a(1) = -3, a(2) = 4, a(n) = -2*(a(n-1) + a(n-2) + a(n-3)) for n > 2. - _Jinyuan Wang_, Apr 07 2020 %o A078071 (PARI) Vec((1-x)/(1+2*x+2*x^2+2*x^3) + O(x^50)) \\ _Jinyuan Wang_, Apr 07 2020 %Y A078071 First differences of A077993. %K A078071 sign,easy %O A078071 0,2 %A A078071 _N. J. A. Sloane_, Nov 17 2002