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 A077905 #26 Mar 26 2020 07:17:28
%S A077905 1,0,1,1,0,2,0,1,2,-1,3,0,0,4,-3,4,1,-3,8,-6,4,5,-10,15,-9,0,16,-24,
%T A077905 25,-8,-15,41,-48,34,8,-55,90,-81,27,64,-144,172,-107,-36,209,-315,
%U A077905 280,-70,-244,525,-594,351,175,-768,1120,-944,177,944,-1887,2065,-1120,-766,2832,-3951,3186,-353,-3597,6784,-7136
%N A077905 Expansion of 1/(1 - x^2 - x^3 + x^4).
%H A077905 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,1,-1).
%F A077905 a(n) = sum(k=1..n/2, sum(j=0..k, binomial(j,n-4*k+2*j)*(-1)^(k-j)*binomial(k,j))), n>0, a(0)=1. - _Vladimir Kruchinin_, Oct 21 2011
%F A077905 a(-3-n) = -A023434(n) for all n in Z. - _Michael Somos_, Sep 25 2014
%e A077905 G.f. = 1 + x^2 + x^3 + 2*x^5 + x^7 + 2*x^8 - x^9 + 3*x^10 + 4*x^13 + ...
%t A077905 CoefficientList[ Series[1/((1 - x) (1 + x - x^3)), {x, 0, 68}], x] (* _Robert G. Wilson v_, Oct 29 2011 *)
%Y A077905 Cf. A023434.
%K A077905 sign,easy
%O A077905 0,6
%A A077905 _N. J. A. Sloane_, Nov 17 2002