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A317985 Number of self-avoiding planar walks starting at (0,0), ending at (n,0), remaining in the first quadrant and using steps (0,1), (1,0), (1,1), (-1,1), and (1,-1) such that (0,1) is never used directly before or after (1,0) or (1,1). 3
1, 2, 7, 38, 284, 2691, 30890, 416449, 6448243, 112751661, 2197200541, 47214026822, 1109022356759, 28269085769331, 777140210643254, 22918982645377342, 721764216387297451, 24173661551378798838, 857993099925433301350, 32168967331652245055171 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..403

MAPLE

a:= proc(n) option remember; `if`(n<4, [1, 2, 7, 38][n+1],

      2*n*a(n-1) -(n-2)*a(n-2) -(2*n-5)*a(n-3))

    end:

seq(a(n), n=0..25);

CROSSREFS

Cf. A277358, A320512.

Sequence in context: A088792 A114160 A145159 * A084552 A094664 A001858

Adjacent sequences:  A317982 A317983 A317984 * A317986 A317987 A317988

KEYWORD

nonn,walk

AUTHOR

Alois P. Heinz, Oct 02 2018

STATUS

approved

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Last modified February 23 12:03 EST 2019. Contains 320431 sequences. (Running on oeis4.)