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 A170813 #3 Mar 31 2012 12:35:36 %S A170813 1,2,4,12,40,116,200,444,760,2160,4368,7852,12828,17252,19612,21104, %T A170813 19760,20392,20128,20636,22408,23988 %N A170813 Number of permutations of 1..n with all differences of elements separated by distances 1 through 7 being respectively unique. %C A170813 (Empirical) Equals A008404 for n<=2m+2, where m is the maximum difference separation 7. %K A170813 nonn %O A170813 1,2 %A A170813 _R. H. Hardin_ Dec 02 2009