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 A081293 #22 Jul 23 2020 12:00:57 %S A081293 2,3,6,14,37,107,329,1055,3486,11780,40510,141286,498524,1776312, %T A081293 6382292,23097542,84118037,308049947,1133682557,4190570237, %U A081293 15551547887,57919961507,216418821767,811055485427,3047804166425,11481792822005 %N A081293 a(n) = A000108(n) + A014137(n). %H A081293 Guo-Niu Han, <a href="/A196265/a196265.pdf">Enumeration of Standard Puzzles</a>, 2011. [Cached copy] %H A081293 Guo-Niu Han, <a href="https://arxiv.org/abs/2006.14070">Enumeration of Standard Puzzles</a>, arXiv:2006.14070 [math.CO], 2020. %F A081293 a(n) = 2*A000108(n) + A014137(n-1). - _Michel Marcus_, Apr 28 2020 %o A081293 (PARI) Cat(n) = binomial(2*n, n)/(n+1); \\ A000108 %o A081293 a(n) = Cat(n)+sum(k=0, n, Cat(k)); \\ _Michel Marcus_, Apr 28 2020 %Y A081293 Cf. A000108, A014137, A081289. %K A081293 nonn %O A081293 0,1 %A A081293 _Antti Karttunen_, Mar 17 2003