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A212589 Walks with n steps on the x-axis using steps {1,0,-1} and visiting no point more than twice. 5
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 (list; graph; refs; listen; history; text; internal format)
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 * A081489 A055278 A293349

Adjacent sequences:  A212586 A212587 A212588 * A212590 A212591 A212592

KEYWORD

nonn,walk

AUTHOR

David Scambler, May 22 2012

STATUS

approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)