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 A177526 Number of permutations of {1,...,n} avoiding adjacent step pattern up, down, down, up, down. 2
 1, 1, 2, 6, 24, 120, 680, 4480, 33600, 285434, 2684680, 27812170, 313926560, 3842611240, 50625902600, 714873188122, 10764733339179, 172258243070682, 2918333808555034, 52191694000877878, 982479378895814520, 19419959862935129834, 402131210857811703926 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..170 FORMULA a(n) ~ c * d^n * n!, where d = 0.94123983763344712685016041467..., c = 1.3558011859159420827133973526... . - Vaclav Kotesovec, Jan 17 2015 MAPLE b:= proc(u, o, t) option remember; `if`(t>5, 0, `if`(u+o=0, 1, add(b(u-j, o+j-1, [1, 3, 4, 1, 6][t]), j=1..u)+ add(b(u+j-1, o-j, [2, 2, 2, 5, 2][t]), j=1..o))) end: a:= n-> `if`(n=0, 1, add(b(j-1, n-j, 1), j=1..n)): seq(a(n), n=0..25); # Alois P. Heinz, Oct 21 2013 MATHEMATICA b[u_, o_, t_] := b[u, o, t] = If[t > 5, 0, If[u + o + t < 6, (u + o)!, Sum[b[u - j, o + j - 1, {1, 3, 4, 1, 6}[[t]]], {j, 1, u}] + Sum[b[u + j - 1, o - j, {2, 2, 2, 5, 2}[[t]]], {j, 1, o}]]]; a[n_] := b[n, 0, 1]; Table[a[n], {n, 0, 25}] (* Jean-François Alcover, Apr 19 2022, after Alois P. Heinz *) CROSSREFS Columns k=18,22 of A242784. Sequence in context: A152340 A152347 A228393 * A214611 A177528 A177527 Adjacent sequences: A177523 A177524 A177525 * A177527 A177528 A177529 KEYWORD nonn AUTHOR R. H. Hardin, May 10 2010 EXTENSIONS a(17)-a(22) from Alois P. Heinz, Oct 21 2013 STATUS approved

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Last modified June 9 23:59 EDT 2023. Contains 363183 sequences. (Running on oeis4.)