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A264077 Number of permutations of [n] with exactly two (possibly overlapping) occurrences of the consecutive step pattern up, down, up, down. 2

%I #10 Nov 02 2015 18:17:01

%S 272,4352,42880,530432,7662336,101713920,1402932224,21604831232,

%T 343423787008,5608501018624,97560785780736,1783363198386176,

%U 33762252617416704,668148809474244608,13830009274919288832,297227159309157138432,6632506903059366936576

%N Number of permutations of [n] with exactly two (possibly overlapping) occurrences of the consecutive step pattern up, down, up, down.

%H Alois P. Heinz, <a href="/A264077/b264077.txt">Table of n, a(n) for n = 7..460</a>

%p b:= proc(u, o, t, c) option remember; `if`(c>2, 0, `if`(u+o=0,

%p `if`(c=2, 1, 0), add(b(u-j, o-1+j, [2,2,4,2][t], c), j=1..u)+

%p add(b(u+j-1, o-j, [1,3,1,3][t], c+`if`(t=4,1,0)), j=1..o)))

%p end:

%p a:= n-> b(0, n, 1, 0);

%p seq(a(n), n=7..25); # _Alois P. Heinz_, Nov 02 2015

%Y Column k=2 of A230797.

%K nonn

%O 7,1

%A _Alois P. Heinz_, Nov 02 2015

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Last modified March 18 22:34 EDT 2024. Contains 370951 sequences. (Running on oeis4.)