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 A131810 #6 Dec 21 2017 04:38:01 %S A131810 0,0,0,0,1,1,1,2,1,2,3,2,2,2,2,2,2,2,2,2,2,3,3,2,2,2,2,3,3,3,3,3,3,3, %T A131810 3,3,2,3,3,3,3,2,3,2,2,3,2,2,2,2,2,2,2,2,2,3,3,3,2,2,2,2,3,3,3,3,3,3, %U A131810 2,2,2,3,2,3,2,2,2,3,3,2,2,2,3,2,4,3,2,3 %N A131810 Additive persistence of Catalan numbers. %e A131810 Catalan number 429 -> 4+2+9=15 -> 1+5=6 thus persistence is 2 %p A131810 with(numtheory): with(combinat): P:=proc(n) local a,t; t:=0; a:=(2*n)!/(n!*(n+1)!); while a>9 do t:=t+1; a:=convert(convert(a,base,10),`+`); od; t; %p A131810 end: seq(P(i),i=0..10^2); %Y A131810 Cf. A003001, A006050, A000108, A131809. %K A131810 easy,nonn,base %O A131810 0,8 %A A131810 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jul 18 2007 %E A131810 Corrected entries and Maple code by _Paolo P. Lava_, Dec 19 2017