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 A120997 #4 Mar 31 2012 13:20:12 %S A120997 1,9,81,729,6561,19683,177147,1594323,43046721,387420489,3486784401, %T A120997 31381059609,282429536481,2541865828329,2541865828329,22876792454961, %U A120997 205891132094649,5559060566555523,50031545098999707 %N A120997 Denominators of partial sums of Catalan numbers scaled by powers of 1/9. %C A120997 Numerators are given under A120996. %C A120997 See A120996 for details and a W. Lang link found there for the definition of four p-families of such scaled Catalan sums. %F A120997 a(n)=denominator(r(n)) with r(n) := rI(p=1,n) = sum(C(k)/L(2)^(2*k),k=0..n), with Lucas L(2)=3 and C(k):=A000108(k) (Catalan). %K A120997 nonn,frac,easy %O A120997 0,2 %A A120997 _Wolfdieter Lang_, Aug 16 2006