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 A275943 #9 Dec 10 2016 14:34:07 %S A275943 1,2,6,19,61,197,640,2091,6860,22566,74365,245397,810639,2680025, %T A275943 8865866 %N A275943 Number of prefix-closed polyominoes of area n. %H A275943 Enrico Formenti and Paolo Massazza, <a href="https://www.researchgate.net/publication/303836692_From_Tetris_to_polyominoes_generation">From Tetris to Polyominoes Generation</a>, Proceedings of GASCom 2016 conference, 2016. %Y A275943 Cf. A000105, A001168. %K A275943 nonn,more %O A275943 1,2 %A A275943 _Enrico Formenti_, Aug 13 2016