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

Author

Clark Kimberling

Keywords

• nonn

Comments

First differences of A025182.

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