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 A027021 #5 Mar 30 2012 18:56:13 %S A027021 1,1,6,7,36,56,181,317,826,1531,3576,6832,15021,29201,61966,121727, %T A027021 252796,499816,1024101,2033077,4130226,8220851,16609456,33115232, %U A027021 66669661,133067881,267285606,533860567,1070731476,2139602456 %N A027021 a(n) = T(n,n) + T(n,m+1) + ... + T(n,n), where m=[ (n+2)/2 ], T given by A027011. %F A027021 G.f.: x(-4x^6+10x^4-x^3-x+1)/[(1-x^2)(1-2x)(1+x-x^2)(1-x-x^2)]. %K A027021 nonn %O A027021 1,3 %A A027021 _Clark Kimberling_