A107761
Number of permutations of (1,3,5,7,9,...,2n-1) where every adjacent pair in the permutation are coprime.
Original entry on oeis.org
1, 2, 6, 24, 72, 480, 3600, 9600, 108000, 1270080, 4795200, 74088000, 768539520, 4759413120, 94182359040, 1893397524480, 11353661706240, 122634632171520, 3104438623534080, 23063946114908160, 664424069072117760
Offset: 1
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.
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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)
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
A107763
Number of ways to arrange the numbers (1,3,5,7,9,...,2n-1) in a circle such that every two adjacent numbers are relatively prime.
Original entry on oeis.org
1, 1, 2, 6, 12, 72, 480, 864, 9600, 108000, 312000, 4795200, 46293120, 241056000, 4759413120, 94182359040, 478511953920, 4873965022080, 122634632171520, 799554193966080, 23063946114908160, 664424069072117760, 3198456730188840960, 108184656752428032000, 2657146152621477888000, 22850984107452933734400, 863305241854715928576000, 15282315334192501724774400, 151673086024479840160972800
Offset: 1
Showing 1-3 of 3 results.
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