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 A177518 #14 Aug 21 2014 12:36:27 %S A177518 1,2,6,24,116,672,4536,34944,302896,2916992,30899616,357080064, %T A177518 4470310976,60269056512,870591770496,13414154256384,219604379097856, %U A177518 3806644208863232,69650568655858176,1341477655028219904,27128858382696129536,574755293400886321152 %N A177518 Number of permutations of 1..n avoiding adjacent step pattern up, down, down, down. %H A177518 Alois P. Heinz, <a href="/A177518/b177518.txt">Table of n, a(n) for n = 1..175</a> %F A177518 a(n) ~ c * n! / r^n, where r = 1.03841563726655630653502212237531835609230623619708108964... is the root of the equation cos(r) - sin(r) + exp(-r) = 0, and c = 1.1718801964367046779834894478269895859267745270209175... . - _Vaclav Kotesovec_, Aug 21 2014 %Y A177518 Column k=0 of A242820. %Y A177518 Columns k=8,14 of A242784. %K A177518 nonn %O A177518 1,2 %A A177518 _R. H. Hardin_, May 10 2010 %E A177518 a(18)-a(22) from _Alois P. Heinz_, Oct 06 2013