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

2,2

Links

Table of n, a(n) for n=2..29.

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

Crossrefs

Pairwise sums of A026123.

Sequence in context: A084085 A052985 A052945 * A006574 A053419 A079227

Adjacent sequences: A026285 A026286 A026287 * A026289 A026290 A026291

Keyword

nonn

Author

Clark Kimberling

Status

approved