A333031 - OEIS

%I #8 May 02 2020 05:02:24

%S 3,10,58,183,408,777,1323,2142,3276,4773,6717,9264,12507,16554,21351,

%T 27090,34047,42318,52008,63453,76566,91371,108249,127608,149487,

%U 173982,201072,231225,265002,302487,343857,389856,440175,494670,553611,617610,687477,763320

%N Number of vertices in an equilateral triangle "frame" of size n (see Comments in A328526 for definition).

%C For n<=3 the terms equal A274585(n). See A328526 for images of the triangular frame.

%H Lars Blomberg, <a href="/A333031/b333031.txt">Table of n, a(n) for n = 1..65</a>

%Y Cf. A328526 (regions), A333030 (edges), A333032 (3-gons), A333033 (4-gons),  A331776 (square frame), A274586 (filled triangle).

%K nonn

%O 1,1

%A _Scott R. Shannon_ and _N. J. A. Sloane_, Mar 05 2020

%E a(12) and beyond from _Lars Blomberg_, May 01 2020