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 A078050 #27 Mar 19 2025 09:42:14
%S A078050 1,-2,0,4,-4,-4,12,-4,-20,28,12,-68,44,92,-180,-4,364,-356,-372,1084,
%T A078050 -340,-1828,2508,1148,-6164,3868,8460,-16196,-724,33116,-31668,-34564,
%U A078050 97900,-28772,-167028,224572,109484,-558628,339660,777596,-1456916,-98276,3012108,-2815556,-3208660,8839772
%N A078050 Expansion of (1-x)/(1+x+2*x^2).
%C A078050 INVERTi transform of A005408, (2n + 1) = A078050 signed: (1, 2, 0, -4, -4, 4, 12, 4, -20, -28, ...) = left border of triangle A144106. - _Gary W. Adamson_, Sep 11 2008
%H A078050 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-2).
%F A078050 a(n-1) = Sum_{k=1..n} (-1)^(n-k) * Sum_{i=0..n} binomial(k,n-i) * binomial(k+i-1, 2*k-1). - _Vladimir Kruchinin_, Mar 11 2013
%F A078050 a(n) = A001607(n+1)-A001607(n). - _R. J. Mathar_, Mar 19 2025
%o A078050 (PARI) Vec((1-x)/(1+x+2*x^2)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 23 2012
%Y A078050 Cf. A005408, A144106. - _Gary W. Adamson_, Sep 11 2008
%Y A078050 Cf. A208904.
%K A078050 sign,easy
%O A078050 0,2
%A A078050 _N. J. A. Sloane_, Nov 17 2002