

A053617


Number of permutations of length n which avoid the patterns 1234 and 1324.


3



1, 1, 2, 6, 22, 90, 396, 1837, 8864, 44074, 224352, 1163724, 6129840, 32703074, 176351644, 959658200, 5262988330, 29057961666, 161374413196, 900792925199, 5050924332096, 28434661250454, 160644331001476, 910455895039056, 5174722258676440, 29486753617569684
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OFFSET

0,3


COMMENTS

These permutations have an "enumeration scheme" of depth 4, see D. Zeilberger's article in the links.
G.f. conjectured to be nonDfinite (see Albert et al. link).  Jay Pantone, Oct 01 2015
a(n) is the number of permutations of length n avoiding the partially ordered pattern (POP) {1>2, 1>3, 2>4, 3>4} of length 4. That is, the number of length n permutations having no subsequences of length 4 in which the first element is the largest and the fourth element is the smallest.  Sergey Kitaev, Dec 10 2020


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CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



