A026288 Number of (s(0), s(1), ..., s(n)) such that every s(i) is an integer, s(0) = 0, s(1) = 1, s(n) = 2, |s(i) - s(i-1)| <= 1 for i >= 2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also T(n,n-2), where T is the array in A026268.
1, 2, 5, 14, 38, 104, 285, 784, 2164, 5994, 16658, 46442, 129868, 364182, 1023960, 2886174, 8153952, 23086374, 65497653, 186175794, 530148414, 1512174076, 4320093569, 12360382436, 35414530188, 101603373430, 291864076387, 839402336610
Offset: 2
Keywords
Crossrefs
Pairwise sums of A026123.
Formula
G.f.: 8z^2(1-z)(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^3.
D-finite with recurrence: (n+4)*a(n) +(-5*n-11)*a(n-1) +(5*n+2)*a(n-2) +(5*n-13)*a(n-3) +6*(-n+5)*a(n-4)=0. - R. J. Mathar, Jun 23 2013