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 A177600 #8 Jan 25 2016 15:51:39 %S A177600 1,1,20,1680,354624,151213748,114062310060,139028830444866, %T A177600 256400413791435360,680598969845995094212,2500271405904975564019712 %N A177600 Number of permutations of 3 copies of 1..n avoiding adjacent step pattern up, down, down, down. %Y A177600 Cf. A014606. %K A177600 nonn %O A177600 0,3 %A A177600 _R. H. Hardin_, May 10 2010 %E A177600 a(9)-a(10) from _Alois P. Heinz_, Nov 02 2013