

A201168


The number of permutations avoiding the "boxed" pattern 123.


0



1, 1, 2, 5, 15, 51, 194, 810, 3675, 17935, 93481, 517129, 3021133
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OFFSET

0,3


COMMENTS

The statement in the Avgustinovich, Kitaev and Valyuzhenich paper that a(6) is greater than 303 is easily seen to be wrong, since that would require (among other constraints) that no more than 2 boxed123avoiding permutations of length 5 end in an ascent.  Peter J. Taylor, Apr 27 2015


LINKS



MATHEMATICA

valid[l_] := valid[l] = Which[Length@l<3, True, Length@l==3, !Less@@l, True, valid[Most@l]&&valid[Rest@l]&&valid[DeleteCases[l, Min@l]]&&valid[DeleteCases[l, Max@l]]]; Length@Select[Permutations@Range@#, valid] & /@ Range[0, 9]


CROSSREFS



KEYWORD

nonn,more


AUTHOR



EXTENSIONS



STATUS

approved



