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 A241229 #13 Feb 16 2025 08:33:22 %S A241229 0,8,144,768,2558,6564,14334,27626,48828,80772,126692,190230,275700, %T A241229 388016,532386,714906,941600,1219410,1556184,1959608,2438868,3002700 %N A241229 Number of acute isosceles triangles on a centered hexagonal grid of size n. %C A241229 A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice. %H A241229 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HexNumber.html">Hex Number</a>. %H A241229 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AcuteTriangle.html">Acute Triangle</a>. %H A241229 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IsoscelesTriangle.html">Isosceles Triangle</a>. %F A241229 a(n) = A241228(n) - A241230(n). %Y A241229 Cf. A190317. %K A241229 nonn,more %O A241229 1,2 %A A241229 _Martin Renner_, Apr 17 2014 %E A241229 a(7) from _Martin Renner_, May 31 2014 %E A241229 a(8)-a(22) from _Giovanni Resta_, May 31 2014