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 A238822 #32 Dec 23 2024 14:53:43 %S A238822 1,14,69,188,465,882,1645,2648,4257,6170,9141,12564,17329,22778,30045, %T A238822 38192,48705,60318,74917,90740,110481,131714,157389,184968,217825, %U A238822 252902,294165,337988,388977,442710,505021,570464,645249,723758,812805,906012,1011025,1120658,1243437,1371080 %N A238822 Number of equilateral triangles bounded by the sides and diagonals of a regular 3n-gon. %H A238822 Andrew Howroyd, <a href="/A238822/b238822.txt">Table of n, a(n) for n = 1..100</a> %H A238822 Antreas Hatzipolakis and Giovanni Resta, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2013-April/011012.html">Number of Equilateral Triangles in Regular 3n-gon</a>, Postings to the Sequence Fans Mailing List, Apr 08 2013 %H A238822 Andrew Howroyd, <a href="/A238822/a238822_1.txt">PARI Program</a>, Sep 2024. %H A238822 Giovanni Resta, <a href="/A238822/a238822.png">Illustration for a(3) = 69</a> %F A238822 Conjecture: For odd n, a(n) = n*(n+1)^3/2 - 3*n^2. - _Vilim Lendvaj_, Jul 24 2024 %Y A238822 Cf. A006561. %K A238822 nonn,nice %O A238822 1,2 %A A238822 _N. J. A. Sloane_, Mar 07 2014 %E A238822 a(6)-a(24) from _Luca Petrone_, Mar 28 2017 %E A238822 Corrected and extended by _Vilim Lendvaj_, Jul 24 2024 %E A238822 a(26) onwards from _Andrew Howroyd_, Sep 26 2024