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 A057729 #18 Jul 27 2021 04:00:57 %S A057729 0,0,1,1,1,4,5,16,37,120,345,1181,3844,13429,46736,167172 %N A057729 Number of triangular polyominoes (or polyiamonds) [A000577] with perimeter n. %D A057729 a(10) found by Brendan Owen. %H A057729 Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/Isopoly1s.html">Isometrical Polyiamonds</a> %H A057729 <a href="/A057729/a057729.gif">Picture from Andrew Clarke's page showing the 4 polyiamonds of perimeter 6 and the 5 of perimeter 7.</a> %Y A057729 Cf. A000577, A284869, A316196. %K A057729 nonn,nice,more %O A057729 1,6 %A A057729 _N. J. A. Sloane_, Oct 29 2000 %E A057729 Link updated by _William Rex Marshall_, Dec 16 2009 %E A057729 a(11)-a(12) from _Luca Petrone_, Apr 04 2017 %E A057729 a(12)-a(16) corrected and extended by _John Mason_, Jul 26 2021