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 A173502 #22 May 28 2021 18:37:54 %S A173502 0,0,8,64,292,916,2344,5048,10096,18296,31400,50752,79308,118876, %T A173502 173768,246096,342256,465064,622904,818552,1063756,1361564,1725432, %U A173502 2159384,2682944,3298568,4027776,4873600 %N A173502 Number of concave kites (darts or arrowheads) on an n X n grid (or geoboard). %H A173502 Nathaniel Johnston, <a href="/A173502/a173502.c.txt">C program for computing terms</a> %e A173502 a(1) = 0, since there is only one point on a 1 X 1 grid. %e A173502 a(2) = 0, since the four points on a 2 X 2 grid build a convex quadrilateral. %e A173502 a(3) = 8, since there are two possible forms of darts on a 3 X 3 grid, each can appear in four rotations. %Y A173502 Cf. A189412, A189417. %K A173502 nonn %O A173502 1,3 %A A173502 _Martin Renner_, Apr 29 2011 %E A173502 a(7)-a(28) from _Nathaniel Johnston_, Apr 29 2011