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A212586
Nonnegative walks of length n on the x-axis starting at the origin using steps {1,0,-1} and visiting no point more than twice.
5
1, 2, 6, 13, 29, 60, 128, 269, 569, 1198, 2526, 5321, 11213, 23624, 49776, 104873, 220961, 465546, 980870, 2066613, 4354189, 9173924, 19328720, 40724053, 85802297, 180778518, 380885758, 802495569, 1690793437, 3562365392, 7505616544, 15813728657, 33318250753
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.
FORMULA
G.f.: (1+x^2+x^3-x^5)/(1-2*x-x^2+2*x^3-x^4+x^6).
MATHEMATICA
CoefficientList[Series[ (1+x^2+x^3-x^5)/(1-2*x-x^2+2*x^3-x^4+x^6) , {x, 0, 45}], x]
CROSSREFS
KEYWORD
nonn,easy,walk
AUTHOR
David Scambler, May 22 2012
STATUS
approved