VOOZH about

URL: https://oeis.org/A026126

⇱ A026126 - OEIS

login
A026126
a(n) = number of (s(0),s(1),...,s(n)) such that every s(i) is a nonnegative integer, s(0) = 1, s(n) = 5, |s(1) - s(0)| = 1, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-4), where T is the array in A026120.
2
1, 4, 16, 56, 188, 608, 1922, 5972, 18326, 55704, 168090, 504348, 1506531, 4484208, 13309572, 39414568, 116508361, 343890196, 1013840836, 2986129168, 8788591801, 25850576024, 76000747820, 223361900840, 656270632875, 1927845012756
OFFSET
4,2
FORMULA
G.f.: z^4(1-z)^2M^6, with M the g.f. of the Motzkin numbers (A001006).
Second differences of A005325.
Conjecture: -(n+8)*(n-4)*a(n) +(4*n^2+5*n-73)*a(n-1) +(-2*n^2+13*n+38)*a(n-2) -(4*n+5)*(n-3)*a(n-3) +3*(n-3)*(n-4)*a(n-4)=0. - R. J. Mathar, Jun 10 2013
CROSSREFS
Sequence in context: A261386 A073388 A109634 * A026155 A025182 A057585
KEYWORD
nonn
EXTENSIONS
Corrected by Ralf Stephan, Apr 06 2004
STATUS
approved