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 A133927 #14 Feb 16 2025 08:33:06
%S A133927 1,30,494,6331,36851,95450,122614,940745,5126032,7519204
%N A133927 Numbers k such that the sum of the first k Catalan numbers, C_1 + C_2 + ... + C_k, is divisible by k.
%C A133927 The sum of the first 30 Catalan numbers, 1 + 2 + 5 + ... + 3814986502092304 = 5175497420902740, is divisible by 30, so 30 is a term.
%C A133927 No more terms < 5*10^7. - _Lars Blomberg_, Nov 07 2011
%H A133927 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CatalanNumber.html">Catalan Number</a>
%t A133927 Module[{nn=40000,lst},lst=Thread[{Range[nn],Accumulate[CatalanNumber[Range[nn]]]}]; Position[ lst,_?(Mod[#[[2]],#[[1]]]==0&),1,Heads->False]]//Flatten (* The program generates the first 5 terms of the sequence. *) (* _Harvey P. Dale_, Jun 18 2024 *)
%Y A133927 Cf. A000108, A014138.
%K A133927 hard,more,nonn
%O A133927 1,2
%A A133927 _Ryan Propper_, Jan 07 2008