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 A212587 Walks of length n on the x-axis using steps {1,0,-1} and visiting no point more than twice. 5
 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 (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 FORMULA 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)). MATHEMATICA 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] CROSSREFS Cf. A212584, A212585, A212586, A164392, A212589. Sequence in context: A011797 A051172 A032192 * A118425 A097809 A272144 Adjacent sequences:  A212584 A212585 A212586 * A212588 A212589 A212590 KEYWORD nonn,walk AUTHOR David Scambler, May 22 2012 STATUS approved

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Last modified October 15 10:15 EDT 2019. Contains 328026 sequences. (Running on oeis4.)