A241232 - OEIS

%I #13 Oct 17 2022 14:29:03

%S 0,2,14,49,134,296,580,1034,1720,2691,4043,5841,8193,11178,14935,

%T 19567,25197,31954,40006,49521,60596,73442,88238,105158,124432,146220,

%U 170802,198278,228999,263185,300988,342775,388775,439269,494462,554839,620474,691717,769060,852639

%N Number of acute triangles, distinct up to congruence, on a centered hexagonal grid of size n.

%C A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HexNumber.html">Hex Number</a>.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/AcuteTriangle.html">Acute Triangle</a>.

%F a(n) = A241231(n) - A241233(n) - A241234(n)

%e For n = 2 the two kinds of non-congruent acute triangles are the following:

%e /. *     * .

%e . * *   . . *

%e \. .     * .

%Y Cf. A190021, A241224.

%K nonn

%O 1,2

%A _Martin Renner_, Apr 17 2014

%E a(7) from _Martin Renner_, May 31 2014

%E a(8)-a(18) from _Giovanni Resta_, May 31 2014

%E More terms from _Bert Dobbelaere_, Oct 17 2022