A026087 - OEIS

A026087

a(n) = number of (s(0), s(1), ..., s(n)) such that every s(i) is an integer, s(0) = 0, |s(i) - s(i-1)| = 1 for i = 1,2,3; |s(i) - s(i-1)| <= 1 for i >= 4, s(n) = 4. Also a(n) = T(n,n-4), where T is the array defined in A026082.

1, 2, 9, 28, 93, 294, 925, 2872, 8856, 27136, 82764, 251472, 761774, 2301924, 6941898, 20899680, 62834397, 188690634, 566081421, 1696873148, 5082959517, 15216909686, 45532045749, 136182428520, 407160436435, 1216953379486, 3636353333187

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OFFSET

4,2

LINKS

Table of n, a(n) for n=4..30.

FORMULA

Conjecture: -(n-4)*(n+4)*a(n) +(4*n^2-11*n-27)*a(n-1) +(-2*n^2+29*n-24)*a(n-2) -(4*n+5)*(n-5)*a(n-3) +3*(n-5)*(n-6)*a(n-4)=0. - R. J. Mathar, Jun 23 2013

CROSSREFS

First differences of A026071.

Sequence in context: A360479 A258347 A323957 * A109188 A248437 A002532

Adjacent sequences: A026084 A026085 A026086 * A026088 A026089 A026090

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved