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 A217746 #11 Sep 15 2013 00:55:36 %S A217746 0,0,0,0,7,24,63,120,242,384,650,896,1425,1872,2703 %N A217746 Number of polygonal regions with finite area in the exterior of a regular n-gon with all diagonals drawn. %F A217746 a(n) = A217745(n) - A217748(n) %e A217746 a(7) = 7 since the 28 diagonals of the regular heptagon divide the exterior in 35 regions consisting of seven triangles (with finite area), i.e., 1 triangle (7 times), and 28 regions with infinite area of three different shapes (two 7 times, one 14 times). %e A217746 a(8) = 24 since the 40 diagonals of the regular octagon divide the exterior in 64 regions consisting of 24 polygons (with finite area), i.e., 2 triangles (one 8 times, one 16 times), and 40 regions with infinite area of three different shapes (one 8 times, two 16 times). %e A217746 a(9) = 63 since the 54 diagonals of the regular 9-gon (nonagon) divide the exterior in 117 regions consisting of 63 polygons (with finite area), i.e., 3 triangles (one 9 times, two 18 times) and 2 quadrilaterals (each 9 times), and 54 regions with infinite area of four different shapes (two 9 times, two 18 times). %Y A217746 Cf. A007678, A217745, A217748. %K A217746 nonn %O A217746 3,5 %A A217746 _Martin Renner_, Mar 23 2013