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A212585 Walks of length n on the x-axis using steps {1,-1} and visiting no point more than twice. 5

%I

%S 1,2,4,8,12,18,26,40,56,82,112,162,222,316,432,608,834,1166,1602,2228,

%T 3066,4252,5858,8108,11178,15454,21316,29450,40632,56114,77434,106914,

%U 147550,203696,281134,388082,535636,739368,1020506,1408626,1944266,2683674,3704184

%N Walks of length n on the x-axis using steps {1,-1} and visiting no point more than twice.

%F G.f. (-1-x-2*x^3+3*x^5-2*x^7+x^8)/((-1+x^2)^2 * (-1+x+x^4)).

%F a(0)=1; a(n) = 2*(A212584(n) + sum(j,1-mod(n,2) .. n-3, step+2, A212584(j))).

%t CoefficientList[Series[(-1-x-2*x^3+3*x^5-2*x^7+x^8)/((-1+x^2)^2 * (-1+x+x^4)), {x,0,45}],x]

%Y Cf. A212584, A212586, A212587, A164392, A212589.

%K nonn,walk

%O 0,2

%A _David Scambler_, May 22 2012

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Last modified September 16 10:52 EDT 2019. Contains 327095 sequences. (Running on oeis4.)