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 A124789 #18 Aug 17 2021 19:56:59
%S A124789 1,0,1,0,1,1,1,1,1,2,2,2,2,3,4,4,4,5,7,8,8,9,12,15,16,17,21,27,31,33,
%T A124789 38,48,58,64,71,86,106,122,135,157,192,228,257,292,349,420,485,549,
%U A124789 641,769,905,1034,1190,1410,1674,1939,2224,2600,3084,3613
%N A124789 Expansion of (1+x^2)/(1-x^4-x^5).
%C A124789 Diagonal sums of A124788.
%H A124789 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1,1).
%F A124789 a(n) = Sum_{k=0..floor(n/2)} C(floor(k/2),n-2*k).
%F A124789 a(n) = A017827(n)+A017827(n-2). - _R. J. Mathar_, May 09 2013
%F A124789 a(n) = A103372(n-3) for n >= 4. - _Georg Fischer_, Nov 03 2018
%F A124789 a(n) = (-1)^n*A124746(n). - _R. J. Mathar_, Jun 30 2020
%t A124789 CoefficientList[Series[(1+x^2)/(1-x^4-x^5),{x,0,60}],x] (* or *) LinearRecurrence[ {0,0,0,1,1},{1,0,1,0,1},60] (* _Harvey P. Dale_, Aug 20 2013 *)
%Y A124789 Cf. A017827, A103372.
%K A124789 easy,nonn
%O A124789 0,10
%A A124789 _Paul Barry_, Nov 07 2006