login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A290279 Number of permutations of [n] with a unique pair of orthogonal (diagonal, antidiagonal) X-rays. 2
1, 1, 2, 6, 22, 110, 628, 4396, 34496, 309230, 3069808 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
The X-rays of a permutation are sequences of (diagonal, antidiagonal) sums of the corresponding permutation matrix.
A unique pair of orthogonal (diagonal, antidiagonal) X-rays allows identification of the permutation.
LINKS
C. Bebeacua, T. Mansour, A. Postnikov and S. Severini, On the X-rays of permutations, arXiv:math/0506334 [math.CO], 2005.
Wikipedia, Permutation
EXAMPLE
a(4) = 22. All permutations of {1,2,3,4} have unique pairs of orthogonal X-rays except 2413 and 3142, which share the same pair (0110110, 0110110):
.
. 0110110 . 0110110
. \\\+--\-+ . \\\+--\-+
. 2 \\| 1 | . 3 \\| 1 |
. 4 \| 1| . 1 \|1 |
. 1 /|1 | . 4 /| 1|
. 3 //| 1 | . 2 //| 1 |
. ///+--/-+ . ///+--/-+
. 0110110 . 0110110
CROSSREFS
Sequence in context: A129535 A216720 A174074 * A014371 A111280 A095817
KEYWORD
nonn,more
AUTHOR
Alois P. Heinz, Jul 25 2017
STATUS
approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)