Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #11 Jan 17 2021 11:23:11
%S 1,12,28,102,187,462,868,1590,3046,4398,6541,8646,12256,15336,20947,
%T 26610,33478,41832,50821,64710,77110,97878,113932,136560,160849,
%U 185220,216286,246450,289945,324594,372976,426936,472231,537366,598606,685650,762736,858546,943684,1043442,1143751,1258800
%N The number of regions inside a concave circular triangle formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.
%C The terms are from numeric computation - no formula for a(n) is currently known.
%H Scott R. Shannon, <a href="/A340685/a340685.png">Regions for n = 2</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_1.png">Regions for n = 3</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_2.png">Regions for n = 4</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_3.png">Regions for n = 6</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_4.png">Regions for n = 8</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_5.png">Regions for n = 10</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_6.png">Regions for n = 14</a>.
%H Scott R. Shannon, <a href="/A340685/a340685_7.png">Regions for n = 15</a>.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Circular_triangle">Circular triangle</a>.
%Y Cf. A340686 (vertices), A340687 (edges), A340688 (n-gons), A340639, A007678, A092867.
%K nonn
%O 1,2
%A _Scott R. Shannon_ and _N. J. A. Sloane_, Jan 16 2021