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 A189414 #21 Feb 16 2025 08:33:14 %S A189414 0,1,94,1758,13698,70539,266320,837060,2260984,5460657,12046294, %T A189414 24775158,47847538,87967579,154764912,262110940,429480216,684015621, %U A189414 1061192670,1609449754,2390049498,3483126407 %N A189414 Number of quadrilaterals on an n X n grid (or geoboard). %H A189414 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Quadrilateral.html">Quadrilateral</a>. %F A189414 a(n) = A189412(n) + A189413(n). %Y A189414 Cf. A175383, A189345, A189412, A189413. %K A189414 nonn %O A189414 1,3 %A A189414 _Martin Renner_, Apr 21 2011 %E A189414 a(6) - a(22) from _Nathaniel Johnston_, Apr 25 2011 %E A189414 a(7) - a(22) corrected by _Michal Forisek_, Sep 06 2011