cp's OEIS Frontend

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

%I A264077 #10 Nov 02 2015 18:17:01
%S A264077 272,4352,42880,530432,7662336,101713920,1402932224,21604831232,
%T A264077 343423787008,5608501018624,97560785780736,1783363198386176,
%U A264077 33762252617416704,668148809474244608,13830009274919288832,297227159309157138432,6632506903059366936576
%N A264077 Number of permutations of [n] with exactly two (possibly overlapping) occurrences of the consecutive step pattern up, down, up, down.
%H A264077 Alois P. Heinz, <a href="/A264077/b264077.txt">Table of n, a(n) for n = 7..460</a>
%p A264077 b:= proc(u, o, t, c) option remember; `if`(c>2, 0, `if`(u+o=0,
%p A264077      `if`(c=2, 1, 0), add(b(u-j, o-1+j, [2,2,4,2][t], c), j=1..u)+
%p A264077       add(b(u+j-1, o-j, [1,3,1,3][t], c+`if`(t=4,1,0)), j=1..o)))
%p A264077     end:
%p A264077 a:= n-> b(0, n, 1, 0);
%p A264077 seq(a(n), n=7..25);  # _Alois P. Heinz_, Nov 02 2015
%Y A264077 Column k=2 of A230797.
%K A264077 nonn
%O A264077 7,1
%A A264077 _Alois P. Heinz_, Nov 02 2015