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 A217720 #20 May 14 2022 04:55:19 %S A217720 2,8,28,116,474,2001,8508,37162,163730,729683,3269602,14773831 %N A217720 Number of one-sided polydrafters with n cells. %C A217720 A polydrafter is a plane figure formed by joining equal triangles with angles of 30, 60, and 90 degrees with certain restrictions on how they are joined. See A056842 for details. One-sided means that distinct mirror images are counted separately. %C A217720 For odd n, an n-drafter cannot have mirror symmetry, so odd entries in this sequence are double those in A056842. %D A217720 Ed Pegg, Jr., Polyform puzzles, in Tribute to a Mathemagician, Peters, 2005, pp. 119-125. %H A217720 K. Ishino, <a href="http://puzzlewillbeplayed.com/Polydrafters/">Polydrafters</a> %H A217720 Bernd Karl Rennhak, <a href="http://www.logelium.de/Drafter/PolyDrafter_EN.htm">Drafter</a> %e A217720 There are 6 two-sided didrafters, two have distinct mirror images, so there are 8 one-sided didrafters. Thus a(2) = 8. %Y A217720 Cf. A056842 (number of two-sided polydrafters). %K A217720 nonn,more %O A217720 1,1 %A A217720 _George Sicherman_, Mar 21 2013 %E A217720 a(8)-a(12) from _Aaron N. Siegel_, May 13 2022