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 A177524 Number of permutations of {1,...,n} avoiding adjacent step pattern up, down, down, down, down. 2
 1, 1, 2, 6, 24, 120, 715, 4970, 39480, 352800, 3502800, 38255900, 455795100, 5883052500, 81774966000, 1217871018000, 19346879737625, 326549862671250, 5835951345093750, 110091785625495000, 2186122850020215000, 45580964489553559375, 995625115672520581250 (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 = 0.9928637443921790380857377558103269268777241137790934589694993..., c = 1.0369478195304845650491426260146999487076420703190374702807322... . - Vaclav Kotesovec, Aug 29 2014 MAPLE b:= proc(u, o, t) option remember; `if`(t>5, 0, `if`(u+o=0, 1, add(b(u-j, o+j-1, `if`(t=1, 1, t+1)), j=1..u)+ add(b(u+j-1, o-j, 2), 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 == 0, 1, Sum[b[u - j, o + j - 1, If[t == 1, 1, t + 1]], {j, 1, u}] + Sum[b[u + j - 1, o - j, 2], {j, 1, o}]]]; a[n_] := If[n == 0, 1, Sum[b[j - 1, n - j, 1], {j, 1, n}]]; Table[a[n], {n, 0, 25}] (* Jean-François Alcover, Apr 20 2022, after Alois P. Heinz *) CROSSREFS Columns k=16,30 of A242784. Sequence in context: A177531 A121987 A324132 * A223905 A164872 A226437 Adjacent sequences: A177521 A177522 A177523 * A177525 A177526 A177527 KEYWORD nonn AUTHOR R. H. Hardin, May 10 2010 EXTENSIONS a(17)-a(22) from Alois P. Heinz, Oct 20 2013 STATUS approved

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Last modified March 25 23:47 EDT 2023. Contains 361529 sequences. (Running on oeis4.)