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

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A092254 Number of permutations of 1,...,2n with alternate odd/even entries that have no adjacent members. 1
0, 0, 0, 10, 226, 8600, 433220, 28226254 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

The 10 for a(4) are:

[7, 4, 1, 6, 3, 8, 5, 2]

[5, 2, 7, 4, 1, 8, 3, 6]

[5, 2, 7, 4, 1, 6, 3, 8]

[1, 4, 7, 2, 5, 8, 3, 6]

[3, 8, 5, 2, 7, 4, 1, 6]

[3, 6, 1, 4, 7, 2, 5, 8]

[5, 8, 3, 6, 1, 4, 7, 2]

[3, 6, 1, 8, 5, 2, 7, 4]

[1, 6, 3, 8, 5, 2, 7, 4]

[7, 2, 5, 8, 3, 6, 1, 4]

PROG

(PARI) { for (i=1, 6, c=0; for (j=1, i!, for (k=1, i!, x=numtoperm(i, j); y=numtoperm(i, k); v=vector(2*i); forstep (z=1, 2*i, 2, v[z]=x[(z+1)/2]*2-1); forstep (z=2, 2*i, 2, v[z]=y[z/2]*2); fl=1; for (z=1, 2*i-1, if (v[z]==v[z+1]+1, fl=0; break); if (v[z]==v[z+1]-1, fl=0; break)); if (fl==1, c++))); print1(", "c)) }

CROSSREFS

Cf. A090931.

Sequence in context: A229256 A342601 A052789 * A211079 A211084 A302095

Adjacent sequences:  A092251 A092252 A092253 * A092255 A092256 A092257

KEYWORD

nonn

AUTHOR

Jon Perry, Feb 20 2004

EXTENSIONS

a(7)-a(8) from Alois P. Heinz, Nov 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 1 16:07 EST 2021. Contains 349430 sequences. (Running on oeis4.)