A212589 Walks with n steps on the x-axis using steps {1,0,-1} and visiting no point more than twice.

1, 3, 8, 18, 34, 64, 118, 214, 382, 678, 1198, 2112, 3716, 6532, 11474, 20148, 35370, 62084, 108964, 191234, 335608, 588968, 1033584, 1813832, 3183072, 5585922, 9802630, 17202438, 30188196, 52976614, 92967500, 163146614, 286302374, 502425668, 881695610, 1547267962

Offset

0,2

Comments

Note: a 0 step counts as a visit and a step but does not contribute to the length of the walk.

Links

Table of n, a(n) for n=0..35.

Formula

G.f. -((1+x^2+x^3-3*x^4+2*x^5+x^6-x^7)/((-1+x)^2 * (-1+x+x^2+x^4))).

Mathematica

CoefficientList[Series[ -((1+x^2+x^3-3*x^4+2*x^5+x^6-x^7)/((-1+x)^2 * (-1+x+x^2+x^4))) , {x, 0, 45}], x]

Crossrefs

Cf. A212584, A212585, A212586, A212587, A164392.

Sequence in context: A075342 A083726 A319006 * A367188 A081489 A055278

Adjacent sequences: A212586 A212587 A212588 * A212590 A212591 A212592

Keyword

nonn,walk

Author

David Scambler, May 22 2012

Status

approved