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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A226433 The number of permutations of length n in a particular geometric grid class. 2
1, 2, 6, 19, 56, 157, 428, 1149, 3058, 8097, 21370, 56279, 147990, 388727, 1020252, 2676139, 7016372, 18389377, 48184544, 126229809, 330635974, 865940277, 2267709166, 5938235819, 15549095466, 40713244907, 106599027888, 279100615999, 730736374568, 1913175616597 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This geometric grid class is given by the array [[0,1,0],[0,0,*],[1,-1,0]]. A picture is given in the LINKS section.

LINKS

Table of n, a(n) for n=1..30.

Jay Pantone, The Enumeration of Permutations Avoiding 3124 and 4312, arXiv:1309.0832 [math.CO], (2013)

Jay Pantone, Picture of the geometric grid class

Index entries for linear recurrences with constant coefficients, signature (7,-18,21,-11,2)

FORMULA

G.f.: x*(1-5*x+10*x^2-8*x^3+x^5)/((1-x)^2*(1-2*x)*(1-3*x+x^2)).

a(n) = 2*A001519(n)-2^(n-2)-n+1, n>1. - R. J. Mathar, Aug 31 2013

PROG

(PARI) x='x+O('x^66); Vec((x-5*x^2+10*x^3-8*x^4+x^6)/((1-x)^2*(1-2*x)*(1-3*x+x^2))) \\ Joerg Arndt, Jun 19 2013

CROSSREFS

Sequence in context: A027098 A183305 A192715 * A121483 A077834 A067675

Adjacent sequences:  A226430 A226431 A226432 * A226434 A226435 A226436

KEYWORD

nonn

AUTHOR

Jay Pantone, Jun 06 2013

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified July 26 08:24 EDT 2017. Contains 289799 sequences.