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A026270 Number of (s(0), s(1), ..., s(n)) such that every s(i) is a nonnegative integer, s(0) = 0, s(1) = 1 = s(n), |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-1), where T is the array in A026268. 1
1, 2, 6, 15, 39, 102, 270, 721, 1941, 5262, 14354, 39372, 108528, 300482, 835278, 2330334, 6522882, 18313542, 51559506, 145530291, 411738723, 1167450066, 3316925794, 9441771081, 26923831029, 76901809810, 219992462862, 630245628681, 1808029517585 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,2
LINKS
FORMULA
G.f.: -1 + 4z^2(1-z)(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^2.
Conjecture: (n+3)*a(n) +3*(-n-1)*a(n-1) +(-n-1)*a(n-2) +3*(n-5)*a(n-3)=0. - R. J. Mathar, Jun 23 2013
CROSSREFS
First differences of A026269. Pairwise sums of A026122.
Sequence in context: A094969 A001674 A121331 * A321646 A246563 A259399
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified July 15 14:07 EDT 2024. Contains 374332 sequences. (Running on oeis4.)