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A026018 a(n) = number of (s(0), s(1), ..., s(2n-1)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| = 1 for i = 1,2,...,n, s(0) = 2, s(2n-1) = 7. Also a(n) = T(2n-1,n-3), where T is the array defined in A026009. 1
1, 7, 36, 164, 702, 2898, 11696, 46512, 183141, 716243, 2788060, 10817820, 41880930, 161900910, 625272480, 2413491360, 9313307370, 35936613414, 138680365704, 535290282632, 2066802226236, 7983111461732, 30848211650592 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,2

LINKS

Table of n, a(n) for n=3..25.

FORMULA

Conjecture: -(n+5)*(3*n-37)*a(n) +3*(-n^2-84*n-173)*a(n-1) +2*(32*n^2+295*n+254)*a(n-2) -8*(n+25)*(2*n-5)*a(n-3)=0. - R. J. Mathar, Jun 20 2013

CROSSREFS

First differences if A003518.

Sequence in context: A080420 A243037 A181292 * A085354 A051198 A003516

Adjacent sequences:  A026015 A026016 A026017 * A026019 A026020 A026021

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified October 19 20:05 EDT 2018. Contains 316378 sequences. (Running on oeis4.)