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 A025571 #6 Sep 07 2019 22:03:44 %S A025571 1,3,19,140,1090,8749,71604,593997,4976785,42016975,356879250, %T A025571 3046096983,26105109424,224485080580,1936029865870,16738879226139, %U A025571 145041018993018,1259189426140919,10950454909118725,95374995078513150,831822673255797630,7263789225782699928 %N A025571 a(n) = T(3n,n), where T is the array defined in A025564. %K A025571 nonn %O A025571 1,2 %A A025571 _Clark Kimberling_ %E A025571 More terms from _Sean A. Irvine_, Sep 07 2019