Permutation of odds: Coprime Adjacents

[Max]

Ray Chandler wrote:
> This sequence is the "odd" analog of A076220 which is related to A086595 and A102381.
> 
> Odd analog of A076220 = 1, 2, 6, 24, 72, 480, 3600, 9600, 108000, 1270080,...

  1 2 6 24 72 480 3600 9600 108000 1270080 4795200 74088000 768539520 4759413120 94182359040 1893397524480 11353661706240 122634632171520 3104438623534080

> Odd analog of A086595 = 1, 2, 6, 24, 60, 432, 3360, 6912, 86400, 1080000,...

> Odd analog of A102381 = 1, 1, 2, 6, 12, 72, 480, 864, 9600, 108000,...

Looks like these two should be exchanged since A102381(n)=n*A086595(n) (i.e., elements of A102381 are larger).

Odd analog of A086595:
  1 1 2 6 12 72 480 864 9600 108000 312000 4795200 46293120 241056000 4759413120 94182359040 478511953920 4873965022080 122634632171520 799554193966080

I'm going to extend the original sequences A076220, A086595, and A102381 in OEIS as well.

Max

> I can find none of these sequences in the OEIS.
> 
> Ray Chandler
> 
> -----Original Message-----
> From: zak seidov [mailto:zakseidov at yahoo.com] 
> Sent: Friday, June 10, 2005 2:58 PM
> To: Leroy Quet
> Cc: seqfan at ext.jussieu.fr
> Subject: Re: Permutation of odds: Coprime Adjacents
> 
> With[{n=9},per=Permutations[Range[1,2 n -1,2]];
>   Select[per,Times @@ Table[GCD
> @@Partition[#,2,1][[i]],{i,n-1}]==1&]//Length]
> => 108000
> And for n from 1 to 9 we have (not in OEIS?) 1, 2, 6, 24, 72, 480, 3600, 9600,108000 For n=10 one needs more CP time ;=)
> Zak
> 
> 
> --- Leroy Quet <qq-quet at mindspring.com> wrote:
> 
> 
>>Could someone please calculate/submit the sequence (or is it already 
>>in the OEIS?) where the nth term is the number of permutations of
>>(1,3,5,7,9,...,2n-1) where every adjacent pair in the permutations is 
>>coprime.
>>
>>For example, if n = 5,
>>the permutation (5,3,7,9,1) is counted, but (5,3,9,1,7) is not counted 
>>because 3 and 9 are adjacent.
>>
>>thanks,
>>Leroy Quet
>> 
>>
> 
> 
> 
> 
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