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Number of ways of arranging the numbers 1..n in a circle so that adjacent numbers do not differ by 1 mod n.
4

%I #14 May 17 2022 11:21:47

%S 1,0,0,0,2,6,46,354,3106,29926,315862,3628906,45132474,604534846,

%T 8680957902,133082437730,2169964347282,37505486702678,685046187718022,

%U 13186335387855770,266816610979894058,5662225862272325550

%N Number of ways of arranging the numbers 1..n in a circle so that adjacent numbers do not differ by 1 mod n.

%H <a href="/index/La#lacings">Index entries for sequences related to shoe lacings</a>

%F For n>1, a(n) = 2*A002816(n).

%e a(5) = 2: 1 3 5 2 4, 1 4 2 5 3; a(6) = 6: 1 4 6 2 5 3, 1 5 2 4 6 3, 1 5 3 6 2 4, 1 3 6 4 2 5, 1 4 2 6 3 5, 1 3 5 2 6 4.

%Y Twice A002816.

%Y The sequence n*a(n) is A089222.

%Y See also A078628.

%K nonn

%O 1,5

%A _N. J. A. Sloane_, Dec 11 2002

%E The sequence was missing a zero; also added a cross-reference _Joel B. Lewis_, Jan 28 2010