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A026289 a(n) = number of (s(0), s(1), ..., s(n)) such that every s(i) is an integer, s(0) = 0, s(1) = 1, s(n) = 3, |s(i) - s(i-1)| <= 1 for i >= 2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also a(n) = T(n,n-3), where T is the array in A026268. 0
1, 3, 9, 27, 79, 229, 659, 1889, 5402, 15430, 44054, 125786, 359296, 1026936, 2937444, 8409540, 24097737, 69118635, 198442329, 570286939, 1640469427, 4723363073, 13612376671, 39265012213, 112248893147, 327545797361, 947203621523 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,2

LINKS

Table of n, a(n) for n=3..29.

FORMULA

G.f.: 16z^3(1-z)(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^4.

CROSSREFS

Pairwise sums of A026124.

Sequence in context: A282087 A238440 A269578 * A027129 A077844 A077827

Adjacent sequences:  A026286 A026287 A026288 * A026290 A026291 A026292

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified January 19 20:33 EST 2019. Contains 319310 sequences. (Running on oeis4.)