A107763 -id:A107763 - cp's OEIS frontend

A107761 Number of permutations of (1,3,5,7,9,...,2n-1) where every adjacent pair in the permutation are coprime.

1, 2, 6, 24, 72, 480, 3600, 9600, 108000, 1270080, 4795200, 74088000, 768539520, 4759413120, 94182359040, 1893397524480, 11353661706240, 122634632171520, 3104438623534080, 23063946114908160, 664424069072117760

Offset: 1

Ray Chandler, following a suggestion of Leroy Quet, Jun 11 2005

nonn

Odd analog of A076220.

			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.

Cf. A076220, A086595, A102381, A107762, A107763.

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] (Seidov)

a(1)-a(9) computed by Zak Seidov.

More terms from Max Alekseyev, Jun 11 2005

A107762 Number of permutations of (1,3,5,7,9,...,2n-1) in which every pair of adjacent numbers as well as the first and the last entries are relatively prime.

Original entry on oeis.org

1, 2, 6, 24, 60, 432, 3360, 6912, 86400, 1080000, 3432000, 57542400, 601810560, 3374784000, 71391196800, 1506917744640, 8134703216640, 87731370397440, 2330058011258880, 15991083879321600, 484342868413071360

Offset: 1

Ray Chandler, Jun 11 2005

nonn

Odd analog of A102381. Equals n*A107763(n).

Cf. A076220, A086595, A102381, A107761, A107763.

More terms from Max Alekseyev, Jun 11 2005

cp's OEIS Frontend

A107761 Number of permutations of (1,3,5,7,9,...,2n-1) where every adjacent pair in the permutation are coprime.

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