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 A059996 #7 Jan 30 2024 19:06:46
%S A059996 1,11,112,1125,112514,11251442,11251442132,11251442132429,
%T A059996 112514421324291430,1125144213242914304862,
%U A059996 112514421324291430486216796,11251442132429143048621679658786
%N A059996 Concatenate Catalan numbers (A000108).
%t A059996 Module[{nn=15,cn},cn=CatalanNumber[Range[0,nn-1]];Table[FromDigits[Flatten[IntegerDigits/@ Take[cn,n]]],{n,nn}]] (* _Harvey P. Dale_, Jan 30 2024 *)
%Y A059996 Cf. A000108.
%K A059996 easy,nonn,base
%O A059996 0,2
%A A059996 _Jason Earls_, Mar 14 2001