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 A387209 #16 Aug 23 2025 10:21:47 %S A387209 0,0,0,1,1,1,3,2,4,4,6,5,10,7,12,11,16,13,22,17,26,23,32,27,41,33,47, %T A387209 42,56,48,68,57,77,69,89,78,105,90,117,106,133,118,153,134,169,154, %U A387209 189,170,214,190,234,215,259,235,289,260,314,290,344,315,380 %N A387209 Number of convex polygons with perimeter n on the regular triangular lattice, not counting rotations and reflections as distinct. %C A387209 a(n) also is the number of convex polyiamonds (triangular polyominoes) with perimeter n. %H A387209 Walter Trump, <a href="/A387209/b387209.txt">Table of n, a(n) for n = 0..10000</a> %H A387209 Walter Trump, <a href="/A387209/a387209.pdf">Convex Polyiamonds</a> %H A387209 Walter Trump, <a href="/A387209/a387209.png">Examples for a(3)-a(12)</a> %Y A387209 Cf. A096004 (number of convex polyiamonds with n cells), A284869 (including nonconvex but simply connected polyiamonds with perimeter n), A057729 (including polyiamonds with holes), A036418 (including rotations and reflections but no holes). %K A387209 nonn,new %O A387209 0,7 %A A387209 _Walter Trump_, Aug 22 2025