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 A372615 #12 May 11 2024 20:22:26 %S A372615 7,121,624,2368,7912,17115,38461,63184,115614,170149,285715,371982, %T A372615 588043 %N A372615 Number of regions among all distinct circles that can be constructed from the 3 vertices and the equally spaced 3*n points placed on the sides of an equilateral triangle, using only a compass. %C A372615 A circle is constructed for every pair of the 3 + 3*n points, the first point defines the circle's center while the second the radius distance. %C A372615 The vertices of the initial equilateral triangle are indicated by small circles in the illustrations here. %H A372615 Scott R. Shannon, <a href="/A372615/a372615.jpg">Image for n = 0</a>. %H A372615 Scott R. Shannon, <a href="/A372615/a372615_1.jpg">Image for n = 1</a>. %H A372615 Scott R. Shannon, <a href="/A372615/a372615_2.jpg">Image for n = 2</a>. %H A372615 Scott R. Shannon, <a href="/A372615/a372615_3.jpg">Image for n = 3</a>. %H A372615 Scott R. Shannon, <a href="/A372615/a372615_4.jpg">Image for n = 4</a>. %F A372615 a(n) = A372616(n) - A372614(n) + 1 by Euler's formula. %Y A372615 Cf. A372614 (vertices), A372616 (edges), A372617 (k-gons), A372682 (number of circles), A371374, A353782, A360352. %K A372615 nonn,more %O A372615 0,1 %A A372615 _Scott R. Shannon_, May 07 2024