login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A193775 Number of signed permutations invariant under the reverse complement and avoiding (-2, -1), (-1, 2), and (1, -2). 0
1, 2, 3, 4, 10, 12, 52, 58, 394, 418 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..9.

FORMULA

a(n) = (\lfloor n/2\rfloor)! 2^{\lfloor n/2\rfloor} + \sum_{k=0}^{\lfloor n/2\lceil} k!

EXAMPLE

For n = 3, the permutations are (1, 2, 3), (3, 2, 1), (-1, -2, -3), and (-3, 2, -1).

CROSSREFS

Sequence in context: A005456 A100773 A250112 * A131120 A115195 A095384

Adjacent sequences:  A193772 A193773 A193774 * A193776 A193777 A193778

KEYWORD

nonn

AUTHOR

Andy Hardt, Aug 04 2011

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 January 23 01:15 EST 2020. Contains 331166 sequences. (Running on oeis4.)