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 A027129 #4 Mar 30 2012 18:56:14 %S A027129 1,3,9,27,79,231,672,1951,5662,16439,47776,139025,405110,1182107, %T A027129 3454035,10105373,29600389,86800887,254797772,748646741,2201587214, %U A027129 6479524339,19084115993,56246912653,165882843095,489509315203 %N A027129 a(n) = T(n,n) + T(n,n+1) + ... + T(n,2n), T given by A027113. %K A027129 nonn %O A027129 0,2 %A A027129 _Clark Kimberling_