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 A056783 #36 Jul 02 2025 16:02:00 %S A056783 1,1,3,7,20,62,204,709,2526,9212,33989,126838,476597,1802618,6850969, %T A056783 26153537,100207548,385225375,1485216987,5741272625,22246000726, %U A056783 86383442996,336093551268,1309998354125,5114452295933,19998173607505,78306014924606,307022185565345 %N A056783 Number of diamond polyominoes with n cells. %C A056783 Also the number of polybricks of size n made of Lego. %H A056783 John Mason, <a href="/A056783/b056783.txt">Table of n, a(n) for n = 1..50</a> %H A056783 Ed Pegg, Jr., <a href="http://demonstrations.wolfram.com/PolyformExplorer/">Illustrations of polyforms</a>. %H A056783 M. Keller, <a href="http://www.solitairelaboratory.com/polyenum.html">Counting Polyforms</a>. %H A056783 M. Vicher, <a href="http://www.vicher.cz/puzzle/polyforms.htm">Polyforms</a>. %H A056783 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyrhomb.html">Polyrhomb</a>. %F A056783 a(n) = 2*A006749(n) + A006746(n) + 2*A006748(n) + 2*A006747(n) + A056877(n) + 2*A056878(n) + A144553(n) + A142886(n). - _Andrew Howroyd_, Dec 04 2018 %Y A056783 Cf. A000105, A056780, A057973, A151522. %K A056783 nonn,hard %O A056783 1,3 %A A056783 _James Sellers_, Aug 28 2000 %E A056783 More terms from _Don Reble_, Nov 01 2001 %E A056783 a(15)-a(18) from _Joseph Myers_, Nov 15 2010 %E A056783 Offset corrected and a(19)-a(28) from _Andrew Howroyd_, Dec 04 2018