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, 7, 36, 164, 702, 2898, 11696, 46512, 183141, 716243, 2788060, 10817820, 41880930, 161900910, 625272480, 2413491360, 9313307370, 35936613414, 138680365704, 535290282632, 2066802226236, 7983111461732, 30848211650592

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