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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A189281 Number of permutations p of 1,2,...,n satisfying p(i+2)-p(i)<>2 for all 1<=i<=n-2. 6
1, 1, 2, 5, 18, 75, 410, 2729, 20906, 181499, 1763490, 18943701, 222822578, 2847624899, 39282739034, 581701775369, 9202313110506, 154873904848803, 2762800622799362, 52071171437696453, 1033855049655584786, 21567640717569135515 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) is also number of ways to place n nonattacking pieces rook + semi-leaper[2,2] on an n X n chessboard.

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 0..35

V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)

Vaclav Kotesovec, Mathematica program for this sequence

FORMULA

Asymptotic (V. Kotesovec, Mar 2011): a(n)/n! ~ (1 + 3/n + 2/n^2)/e.

CROSSREFS

Cf. A000255, A002464, A055790, A110128.

Sequence in context: A039744 A319121 A289655 * A006848 A208968 A206293

Adjacent sequences:  A189278 A189279 A189280 * A189282 A189283 A189284

KEYWORD

nonn,hard

AUTHOR

Vaclav Kotesovec, Apr 19 2011

EXTENSIONS

Terms a(33)-a(35) from Vaclav Kotesovec, Apr 20 2012

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 March 25 04:15 EDT 2019. Contains 321457 sequences. (Running on oeis4.)