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A201168 The number of permutations avoiding the "boxed" pattern 123. 0
1, 1, 2, 5, 15, 51, 194, 810, 3675, 17935, 93481, 517129, 3021133 (list; graph; refs; listen; history; text; internal format)
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 boxed-123-avoiding permutations of length 5 end in an ascent. - Peter J. Taylor, Apr 27 2015
LINKS
Sergey Avgustinovich, Sergey Kitaev and Alexander Valyuzhenich, Avoidance of boxed mesh patterns on permutations.
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
Sequence in context: A304454 A287253 A117426 * A001681 A343665 A192553
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, May 06 2012
EXTENSIONS
More terms and Mathematica program from Peter J. Taylor, Apr 27 2015
STATUS
approved

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Last modified May 30 04:46 EDT 2024. Contains 372958 sequences. (Running on oeis4.)