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 A177531 Number of permutations of {1,...,n} avoiding adjacent step pattern up, up, down, down, down. 2
 1, 1, 2, 6, 24, 120, 710, 4900, 38640, 342720, 3376800, 36603975, 432850200, 5545086300, 76500496800, 1130799033000, 17829310686875, 298684478837750, 5298029559119250, 99196696006173000, 1955043380032965000, 40458045505003152500, 877115498011253207500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 FORMULA a(n) ~ c * d^n * n!, where d = 0.9854377717049233842779147747459503689075051143455990422632259770134..., c = 1.077575450109847511736343360036618345267367515043056772740942767... . - Vaclav Kotesovec, Jan 17 2015 MAPLE b:= proc(u, o, t) option remember; `if`(t>5, 0, `if`(u+o+t<6, (u+o)!, add(b(u-j, o+j-1, [1, 1, 4, 5, 6][t]), j=1..u)+ add(b(u+j-1, o-j, [2, 3, 3, 2, 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, 1, 4, 5, 6}[[t]]], {j, 1, u}] + Sum[b[u + j - 1, o - j, {2, 3, 3, 2, 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=24,28 of A242784. Sequence in context: A177530 A324134 A324135 * A121987 A324132 A177524 Adjacent sequences: A177528 A177529 A177530 * A177532 A177533 A177534 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 6 18:49 EDT 2023. Contains 363150 sequences. (Running on oeis4.)