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 A333033 #10 Jun 01 2025 17:39:37 %S A333033 0,0,24,102,252,504,867,1431,2214,3228,4509,6237,8481,11259,14445, %T A333033 18261,22935,28497,34980,42762,51708,61632,72795,85791,100611,117027, %U A333033 134874,154836,177402,202548,230355,261543,295707,332271,371313,413937,460881,511551 %N A333033 Number of quadrilateral regions in an equilateral triangular "frame" of size n (see Comments in A328526 for definition). %C A333033 See A328526 for images of the triangular frame. %H A333033 Lars Blomberg, <a href="/A333033/b333033.txt">Table of n, a(n) for n = 1..65</a> %Y A333033 Cf. A328526 (regions), A333030 (edges), A333031 (vertices), A333032 (3-gons), A331776 (square frame), A274586 (filled triangle). %K A333033 nonn %O A333033 1,3 %A A333033 _Scott R. Shannon_ and _N. J. A. Sloane_, Mar 05 2020 %E A333033 a(12) and beyond from _Lars Blomberg_, May 01 2020