A026290 a(n) = number of (s(0), s(1), ..., s(n)) such that every s(i) is an integer, s(0) = 0, s(1) = 1, s(n) = 4, |s(i) - s(i-1)| <= 1 for i >=2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also a(n) = T(n,n-4), where T is the array in A026268.

1, 4, 14, 46, 145, 446, 1349, 4034, 11966, 35290, 103642, 303458, 886548, 2585922, 7534245, 21934524, 63826041, 185668816, 540034074, 1570719570, 4568920029, 13292253106, 38679350746, 112583530784, 327793747775, 954702193796

Offset

4,2

Links

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

Formula

G.f.: 32z^4(1-z)(1-z^2)/[1-z+sqrt(1-2z-3z^2)]^5.

Crossrefs

Pairwise sums of A026145.

Pairwise sums of A026125.

Sequence in context: A054449 A029868 A030267 * A027649 A330796 A049221

Adjacent sequences: A026287 A026288 A026289 * A026291 A026292 A026293

Keyword

nonn

Author

Clark Kimberling

Status

approved