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 A077899 #13 Aug 13 2024 11:45:48
%S A077899 1,0,3,-3,10,-18,42,-87,190,-405,873,-1872,4024,-8640,18561,-39864,
%T A077899 85627,-183915,395034,-848490,1822474,-3914487,8407926,-18059373,
%U A077899 38789713,-83316384,178955184,-384377664,825604417,-1773314928,3808901427,-8181135699,17572253482,-37743426306
%N A077899 Expansion of (1-x)^(-1)/(1+x-2*x^2+x^3).
%H A077899 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,3,-3,1).
%F A077899 a(n) = (-1)^n * Sum_{k=0..n} binomial(2*k-1,n-k). - _Seiichi Manyama_, Aug 13 2024
%o A077899 (PARI) Vec((1-x)^(-1)/(1+x-2*x^2+x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%o A077899 (PARI) a(n) = (-1)^n*sum(k=0, n, binomial(2*k-1, n-k)); \\ _Seiichi Manyama_, Aug 13 2024
%Y A077899 Cf. A002478.
%K A077899 sign,easy
%O A077899 0,3
%A A077899 _N. J. A. Sloane_, Nov 17 2002