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!)
A191798 Number of essentially different ways of arranging numbers 1 through 2*n around a circle so that the sums of each pair of adjacent numbers are neither all prime nor all composite. 0
0, 2, 58, 2474, 180480, 19895936, 3105348340, 652948189204, 177662757810868, 60772232945639507, 25533219938917963508, 12921764841857675170314, 7754002391777621430686566 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Finding a pattern, recurrence relation or explicit formula for this sequence would allow us to find terms in A191374 using terms from A051252, or vice versa.

LINKS

Table of n, a(n) for n=1..13.

FORMULA

For n>1, a(n) = (2*n-1)!/2 - A051252(n) - A191374(n).

EXAMPLE

a(2) = 2 since the arrangements 1,3,2,4 and 1,3,4,2 both satisfy the condition.

CROSSREFS

Cf. A051252, A191374.

Sequence in context: A285148 A115610 A341082 * A206531 A290306 A113635

Adjacent sequences:  A191795 A191796 A191797 * A191799 A191800 A191801

KEYWORD

nonn,more

AUTHOR

Bennett Gardiner, Jun 16 2011

EXTENSIONS

a(7) corrected, a(8)-a(13) added by Max Alekseyev, Aug 19 2013

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 September 25 07:19 EDT 2022. Contains 356959 sequences. (Running on oeis4.)