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A110128 Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)| not equal to 2 for all 0<i<n-1. 12
1, 1, 2, 4, 16, 44, 200, 1288, 9512, 78652, 744360, 7867148, 91310696, 1154292796, 15784573160, 232050062524, 3648471927912, 61080818510972, 1084657970877416, 20361216987032284, 402839381030339816, 8377409956454452732 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
When n is even: 1) Number of ways that n persons seated at a rectangular table with n/2 seats along the two opposite sides can be rearranged in such a way that neighbors are no more neighbors after the rearrangement. 2) Number of ways to arrange n kings on an n X n board, with 1 in each row and column, which are non-attacking with respect to the main four quadrants.
a(n) is also number of ways to place n nonattacking pieces rook + alfil on an n X n chessboard (Alfil is a leaper [2,2]) [From Vaclav Kotesovec, Jun 16 2010]
Note that the conjectured recurrence was based on the 600-term b-file, not the other way round. - N. J. A. Sloane, Dec 07 2022
LINKS
Rintaro Matsuo, Table of n, a(n) for n = 0..600 (terms up to a(35) from Vaclav Kotesovec)
Roberto Tauraso, The Dinner Table Problem: The Rectangular Case, INTEGERS, vol. 6 (2006), paper A11. arXiv:math/0507293.
FORMULA
A formula is given in the Tauraso reference.
Asymptotic (R. Tauraso 2006, quadratic term V. Kotesovec 2011): a(n)/n! ~ (1 + 4/n + 8/n^2)/e^2.
a(n) ~ exp(-2) * n! * (1 + 4/n + 8/n^2 + 68/(3*n^3) + 242/(3*n^4) + 1692/(5*n^5) + 72802/(45*n^6) + 2725708/(315*n^7) + 16083826/(315*n^8) + 186091480/(567*n^9) + 32213578294/(14175*n^10) + ...), based on the recurrence by Manuel Kauers. - Vaclav Kotesovec, Dec 05 2022
CROSSREFS
Column k=2 of A333706.
Sequence in context: A192890 A062330 A133465 * A370658 A148279 A101061
KEYWORD
nonn,nice
AUTHOR
Roberto Tauraso, A. Nicolosi and G. Minenkov, Jul 13 2005
EXTENSIONS
Edited by N. J. A. Sloane at the suggestion of Vladeta Jovovic, Jan 01 2008
Terms a(33)-a(35) from Vaclav Kotesovec, Apr 20 2012
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)