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 A246574 #17 Nov 10 2024 14:45:31
%S A246574 0,4,20,84,336,1320,5148,20020,77792,302328,1175720,4576264,17829600,
%T A246574 69535440,271455660,1060730100,4148633280,16239715800,63621474840,
%U A246574 249436575960,978650680800,3842267672880,15094623000600,59335590776904,233373427269696
%N A246574 a(n) = 2*(n-1)*Catalan(n).
%H A246574 Vincenzo Librandi, <a href="/A246574/b246574.txt">Table of n, a(n) for n = 1..1000</a>
%H A246574 Igor Pak, <a href="http://arxiv.org/abs/1408.5711">History of Catalan numbers</a>, arXiv:1408.5711 [math.HO], 2014. See Section 5, A_n.
%t A246574 Table[2 (CatalanNumber[n] (n - 1)), {n, 1, 30}] (* _Vincenzo Librandi_, Aug 31 2014 *)
%o A246574 (Magma) [2*(n-1)*Catalan(n): n in [1..30]]; // _Vincenzo Librandi_, Aug 31 2014
%Y A246574 Cf. A000108, A024483.
%K A246574 nonn,easy
%O A246574 1,2
%A A246574 _N. J. A. Sloane_, Aug 30 2014