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A212587
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Walks of length n on the x-axis using steps {1,0,-1} and visiting no point more than twice.
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5
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1, 4, 12, 30, 66, 148, 316, 682, 1438, 3052, 6428, 13574, 28594, 60284, 127004, 267634, 563870, 1188084, 2503180, 5274062, 11112002, 23412164, 49327516, 103929178, 218970366, 461352988, 972033500, 2047996278, 4314962930, 9091278956, 19154591420, 40357179234
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OFFSET
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0,2
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COMMENTS
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Note: a 0 step counts as a visit and a step but does not contribute to the length of the walk.
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LINKS
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FORMULA
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G.f. (-1-2*x-2*x^2-2*x^3+2*x^4-2*x^5-2*x^6-2*x^7+3*x^8) / ((-1+x^2)^2 * (-1+2*x+x^4)).
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MATHEMATICA
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CoefficientList[Series[ (-1-2*x-2*x^2-2*x^3+2*x^4-2*x^5-2*x^6 -2*x^7+3*x^8)/((-1+x^2)^2 * (-1+2*x+x^4)), {x, 0, 45}], x]
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CROSSREFS
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KEYWORD
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nonn,walk
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AUTHOR
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STATUS
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approved
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