This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A290280 Number of pairs of orthogonal (diagonal, antidiagonal) X-rays for all permutations of [n]. 2
 1, 1, 2, 6, 23, 115, 674, 4718, 37371, 335435, 3340116 (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 Wikipedia, Permutation matrix EXAMPLE a(4) = 23.  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 Cf. A289971, A290279. Sequence in context: A117158 A317128 A185334 * A059513 A132647 A177253 Adjacent sequences:  A290277 A290278 A290279 * A290281 A290282 A290283 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 | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 19 03:54 EDT 2018. Contains 313843 sequences. (Running on oeis4.)