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A030435 Expansion of (1+x-2*x^2-x^3)/(1/2-2*x^2+x^4). 1
2, 2, 4, 6, 12, 20, 40, 68, 136, 232, 464, 792, 1584, 2704, 5408, 9232, 18464, 31520, 63040, 107616, 215232, 367424, 734848, 1254464, 2508928, 4283008, 8566016, 14623104, 29246208, 49926400, 99852800 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Also (starting 4,6,...) the number of zig-zag paths from top to bottom of a rectangle of width 7, whose color is that of the top right corner. [From Joseph Myers, Dec 24 2008]

LINKS

Table of n, a(n) for n=0..30.

Joseph Myers, BMO 2008--2009 Round 1 Problem 1---Generalisation

PROG

(PARI) Vec((1+x-2*x^2-x^3)/(1/2-2*x^2+x^4)+O(x^99)) \\ Charles R Greathouse IV, Sep 27 2012

CROSSREFS

a(n)=2 A030436(n).

Sequence in context: A037163 A059123 A001679 * A063886 A003000 A216957

Adjacent sequences:  A030432 A030433 A030434 * A030436 A030437 A030438

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified October 21 06:39 EDT 2019. Contains 328292 sequences. (Running on oeis4.)