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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
1, 2, 4, 8, 12, 18, 26, 40, 56, 82, 112, 162, 222, 316, 432, 608, 834, 1166, 1602, 2228, 3066, 4252, 5858, 8108, 11178, 15454, 21316, 29450, 40632, 56114, 77434, 106914, 147550, 203696, 281134, 388082, 535636, 739368, 1020506, 1408626, 1944266, 2683674, 3704184 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..42.

FORMULA

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

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

MATHEMATICA

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]

CROSSREFS

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

Sequence in context: A293495 A053799 A284122 * A085891 A006501 A224814

Adjacent sequences:  A212582 A212583 A212584 * A212586 A212587 A212588

KEYWORD

nonn,walk

AUTHOR

David Scambler, May 22 2012

STATUS

approved

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Last modified August 23 14:44 EDT 2019. Contains 326249 sequences. (Running on oeis4.)