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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,2

LINKS

Table of n, a(n) for n=4..29.

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

Adjacent sequences:  A026123 A026124 A026125 * A026127 A026128 A026129

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

Corrected by Ralf Stephan, Apr 06 2004

STATUS

approved

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Last modified December 15 11:43 EST 2019. Contains 329999 sequences. (Running on oeis4.)