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 A173434 #8 Jun 29 2021 15:22:35
%S A173434 0,0,0,1,2,4,6,10,16,27,44,72,116,188,304,493,798,1292,2090,3382,5472,
%T A173434 8855,14328,23184,37512,60696,98208,158905,257114,416020,673134,
%U A173434 1089154,1762288,2851443,4613732,7465176
%N A173434 a(n) = (A000045(n)-A173432(n))/2.
%C A173434 Also the NW-SE diagonal sums of A173402.
%H A173434 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,2,0,-1).
%F A173434 a(n) + A173433(n) = A000045(n).
%F A173434 a(n)= 2*a(n-1) -2*a(n-3) +2*a(n-4) -a(n-6). - _R. J. Mathar_, Mar 01 2010
%F A173434 G.f.: x^4 / ( (x-1)*(1+x)*(x^2-x+1)*(x^2+x-1) ). - _R. J. Mathar_, Nov 03 2016
%t A173434 CoefficientList[Series[x^4/((x-1)(1+x)(x^2-x+1)(x^2+x-1)),{x,0,40}],x] (* or *) LinearRecurrence[{2,0,-2,2,0,-1},{0,0,0,0,1,2},40] (* _Harvey P. Dale_, Jun 29 2021 *)
%Y A173434 Cf. A112468, A000045, A173398, A173402
%K A173434 nonn,easy
%O A173434 1,5
%A A173434 _Mark Dols_, Feb 18 2010