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 A128650 #14 Dec 05 2018 08:11:28
%S A128650 0,4,16,60,224,840,3168,12012,45760,175032,671840,2586584,9984576,
%T A128650 38630800,149768640,581690700,2262890880,8815845720,34389986400,
%U A128650 134312002440,525129633600,2055166429680,8050465600320,31561484455800
%N A128650 Number of polygons on n vertices with exactly three faces.
%H A128650 Vincenzo Librandi, <a href="/A128650/b128650.txt">Table of n, a(n) for n = 2..200</a>
%H A128650 T. Mansour and S. Severini, <a href="https://arxiv.org/abs/math/0603225">Grid polygons from permutations and their enumeration by the kernel method</a>, arXiv:math/0603225 [math.CO], 2006.
%F A128650 a(n) = 4*(n-2)/(n-1) * C(2*n-4,n-2).
%F A128650 For n>2, a(n) = 4*A001791(n-2).
%t A128650 Table[4 Binomial[2n-4, n-3], {n, 2, 25}] (* _Jean-François Alcover_, Dec 05 2018 *)
%K A128650 nonn
%O A128650 2,2
%A A128650 _Ralf Stephan_, May 08 2007