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 A170809 #3 Mar 31 2012 12:35:36 %S A170809 1,2,4,12,40,116,200,444,864,3368,10936,38320,139848,534828,2230464, %T A170809 9802612,46188544,231210272,1213437504,6717614708,39002297800 %N A170809 Number of permutations of 1..n with all differences of elements separated by distances 1 through 3 being respectively unique. %C A170809 (Empirical) Equals A008404 for n<=2m+2, where m is the maximum difference separation 3. %K A170809 nonn %O A170809 1,2 %A A170809 _R. H. Hardin_ Dec 02 2009