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 A124751 #4 Mar 10 2017 13:26:57
%S A124751 1,0,1,0,1,0,1,-1,1,-1,1,-1,1,-2,2,-2,2,-2,2,-3,4,-4,4,-4,4,-5,7,-8,8,
%T A124751 -8,8,-9,12,-15,16,-16,16,-17,21,-27,31,-32,32,-33,38,-48,58,-63,64,
%U A124751 -65,71,-86,106,-121,127,-129,136,-157,192,-227,248
%N A124751 Expansion of (1+x^2+x^4)/(1-x^6+x^7).
%C A124751 Diagonal sums of number triangle A124749.
%H A124751 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,1,-1).
%F A124751 a(n)=sum{k=0..floor(n/2), C(floor(k/3),n-2k)*(-1)^n}
%t A124751 CoefficientList[Series[(1+x^2+x^4)/(1-x^6+x^7),{x,0,100}],x] (* or *) LinearRecurrence[{0,0,0,0,0,1,-1},{1,0,1,0,1,0,1},100] (* _Harvey P. Dale_, Mar 10 2017 *)
%K A124751 easy,sign
%O A124751 0,14
%A A124751 _Paul Barry_, Nov 06 2006