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A258216 Number of permutations of {1,2,3,...,n} such that no multiples of 3 are adjacent. 0

%I #11 May 25 2015 19:41:56

%S 1,1,2,6,24,120,480,3600,30240,151200,1693440,20321280,121927680,

%T 1828915200,28740096000,201180672000,3793692672000,73977007104000,

%U 591816056832000,13463815292928000,314155690168320000

%N Number of permutations of {1,2,3,...,n} such that no multiples of 3 are adjacent.

%F a(n) = factorial(n-floor(n/3))*fallfac(n+1-floor(n/3),floor(n/3)), where fallfac is falling factorial, A008279.

%F a(n) ~ n! * 2^(2*n+2-2*floor(n,3)/3) / 3^(n+1/2). - _Vaclav Kotesovec_, May 23 2015

%t Table[Factorial[n-Floor[n/3]]*FactorialPower[n+1-Floor[n/3],Floor[n/3],1], {n, 0, 20}]

%Y Cf. A008279, A010790, A258213.

%K nonn,easy

%O 0,3

%A _Ran Pan_, May 23 2015

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Last modified March 19 02:58 EDT 2024. Contains 370952 sequences. (Running on oeis4.)