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 A306524 Number of permutations p of [n] having at least one index i with |p(i)-i| = 2. 3

%I

%S 0,0,0,3,15,86,544,3934,32079,292509,2952702,32712087,394749367,

%T 5155010088,72440184064,1090017765544,17486996858151,297965879586295,

%U 5374189975316350,102290550351854445,2049025241258716927,43089888746430771294,949172134240270646352

%N Number of permutations p of [n] having at least one index i with |p(i)-i| = 2.

%H Alois P. Heinz, <a href="/A306524/b306524.txt">Table of n, a(n) for n = 0..450</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Permutation">Permutation</a>

%F a(n) = n! - A306523(n).

%e a(3) = 3: 231, 312, 321.

%e a(4) = 15: 1342, 1423, 1432, 2314, 2413, 2431, 3124, 3142, 3214, 3241, 3412, 3421, 4132, 4213, 4312.

%Y Column k=2 of A306506.

%Y Cf. A000142, A306523.

%K nonn

%O 0,4

%A _Alois P. Heinz_, Feb 21 2019

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Last modified December 8 12:07 EST 2019. Contains 329862 sequences. (Running on oeis4.)