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 A216721 #6 Apr 13 2021 19:21:30 %S A216721 2,10,55,356,2723,23300,220997,2308564 %N A216721 Second column of A216719. %D A216721 Wayne M. Dymacek, Isaac Lambert and Kyle Parsons, Arithmetic Progressions in Permutations, http://math.ku.edu/~ilambert/CN.pdf, 2012. %Y A216721 Cf. A174074, A216719. %K A216721 nonn %O A216721 5,1 %A A216721 _N. J. A. Sloane_, Sep 15 2012