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 A177549 #18 Nov 11 2016 21:37:38
%S A177549 1,1,2,6,24,120,720,4969,39184,347544,3424320,37150741,439774085,
%T A177549 5639099103,77873192126,1152123776419,18181366630226,304851804959519,
%U A177549 5412206888619242,101424438933572112,2000731009697485843,41440364401733715980,899211137893661967405
%N A177549 Number of permutations of {1,...,n} avoiding adjacent step pattern up, up, down, down, up, up.
%H A177549 Alois P. Heinz, <a href="/A177549/b177549.txt">Table of n, a(n) for n = 0..450</a>
%F A177549 a(n) ~ c * d^n * n!, where d = 0.986314277283772995320277545416339641125925..., c = 1.08332315844132327949722334709840176297166... . - _Vaclav Kotesovec_, Jan 17 2015
%p A177549 b:= proc(u, o, t) option remember; `if`(t>6, 0, `if`(u+o+t<7, (u+o)!,
%p A177549 add(b(u-j, o+j-1, [1, 1, 4, 5, 1, 1][t]), j=1..u)+
%p A177549 add(b(u+j-1, o-j, [2, 3, 3, 2, 6, 7][t]), j=1..o)))
%p A177549 end:
%p A177549 a:= n-> b(n, 0, 1):
%p A177549 seq(a(n), n=0..25); # _Alois P. Heinz_, Oct 23 2013
%t A177549 b[u_, o_, t_] := b[u, o, t] = If[t>6, 0, If[u+o+t<7, (u+o)!, Sum[b[u-j, o+j-1, {1, 1, 4, 5, 1, 1}[[t]]], {j, 1, u}] + Sum[b[u+j-1, o-j, {2, 3, 3, 2, 6, 7}[[t]]], {j, 1, o}]]]; a[n_] := b[n, 0, 1]; Table[a[n], {n, 0, 25}] (* _Jean-François Alcover_, Nov 11 2016, after _Alois P. Heinz_ *)
%Y A177549 Column k=51 of A242784.
%K A177549 nonn
%O A177549 0,3
%A A177549 _R. H. Hardin_, May 10 2010
%E A177549 a(17)-a(22) from _Alois P. Heinz_, Oct 23 2013