A026071 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; |s(i) - s(i-1)| <= 1 for i >= 3, s(n) = 4. Also a(n) = T(n,n-4), where T is the array defined in A024996.

1, 3, 12, 40, 133, 427, 1352, 4224, 13080, 40216, 122980, 374452, 1136226, 3438150, 10380048, 31279728, 94114125, 282804759, 848886180, 2545759328, 7628718845, 22845628531, 68377674280, 204560102800, 611720539235, 1828673918721

Offset

4,2

Comments

First differences of A025182.

Links

Table of n, a(n) for n=4..29.

Formula

Conjecture: -(n-4)*(n+4)*a(n) +(4*n+7)*(n-4)*a(n-1) +(-2*n^2+23*n-12)*a(n-2) -(4*n+3)*(n-4)*a(n-3) +3*(n-4)*(n-5)*a(n-4)=0. - R. J. Mathar, Jun 22 2013

Crossrefs

Sequence in context: A027991 A120304 A289652 * A102839 A050182 A222610

Adjacent sequences: A026068 A026069 A026070 * A026072 A026073 A026074

Keyword

nonn

Author

Clark Kimberling

Status

approved