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 A347521 #15 Sep 08 2021 03:47:04 %S A347521 1,0,1,1,3,3,11,17,40,69,152,309,736,1682,3984,9031 %N A347521 Number of polyominoes with n cells formed by coordinates that are not coprime. %C A347521 By considering cells of a square grid, whose coordinates are not coprime (i.e., gcd(m,n) > 1), we get figures called polyominoes. Among all possible free polyominoes, only a few can be found following this rule. %H A347521 Ludovic Schwob, <a href="/A347521/a347521.pdf">Illustration of a(12)</a> %Y A347521 Cf. A000105. %K A347521 nonn,more %O A347521 1,5 %A A347521 _Ludovic Schwob_, Sep 04 2021