login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Table of n, a(n) for n=0..12.

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 A192553 A053553

Adjacent sequences:  A201165 A201166 A201167 * A201169 A201170 A201171

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 04:33 EDT 2019. Contains 328026 sequences. (Running on oeis4.)