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 A239658 #29 May 22 2022 16:43:42 %S A239658 1,1,3,11,75,528,4584,40609,373981,3493723,33079702,316109657, %T A239658 3044648053 %N A239658 Number of free triangular n-polyplets (triangular polyominoes connected at edges or corners), where turning over is allowed and holes are allowed. %C A239658 We get triangular polyominoes when connecting over edges only (rather than edges and corners); that is A000577. The square equivalent (that is, n-polyplets) is A030222. The neighborhood is also known as the Triangular Moore neighborhood, and equals the moves of the Tri-Chess king. %Y A239658 Cf. A000577, A030222. %K A239658 nonn,hard,more %O A239658 0,3 %A A239658 _Abe Wits_ and Ragnar Groot Koerkamp, Nov 20 2020 %E A239658 a(11) and a(12) from _Aaron N. Siegel_, May 22 2022