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 A241232 #14 Feb 16 2025 08:33:22 %S A241232 0,2,14,49,134,296,580,1034,1720,2691,4043,5841,8193,11178,14935, %T A241232 19567,25197,31954,40006,49521,60596,73442,88238,105158,124432,146220, %U A241232 170802,198278,228999,263185,300988,342775,388775,439269,494462,554839,620474,691717,769060,852639 %N A241232 Number of acute triangles, distinct up to congruence, on a centered hexagonal grid of size n. %C A241232 A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice. %H A241232 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HexNumber.html">Hex Number</a>. %H A241232 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AcuteTriangle.html">Acute Triangle</a>. %F A241232 a(n) = A241231(n) - A241233(n) - A241234(n) %e A241232 For n = 2 the two kinds of non-congruent acute triangles are the following: %e A241232 /. * * . %e A241232 . * * . . * %e A241232 \. . * . %Y A241232 Cf. A190021, A241224. %K A241232 nonn %O A241232 1,2 %A A241232 _Martin Renner_, Apr 17 2014 %E A241232 a(7) from _Martin Renner_, May 31 2014 %E A241232 a(8)-a(18) from _Giovanni Resta_, May 31 2014 %E A241232 More terms from _Bert Dobbelaere_, Oct 17 2022