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 A170808 #3 Mar 31 2012 12:35:36 %S A170808 1,2,4,12,40,116,252,768,2704,12756,63168,338308,1956876,11971780, %T A170808 77909884,535178056,3906154920,30146769464,244980749052,2094507398508 %N A170808 Number of permutations of 1..n with all differences of elements separated by distances 1 or 2 being respectively unique. %C A170808 (Empirical) Equals A008404 for n<=2m+2, where m is the maximum difference separation 2. %K A170808 nonn %O A170808 1,2 %A A170808 _R. H. Hardin_ Dec 02 2009