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A118649 Row sums for A106597. 1
1, 2, 5, 12, 30, 74, 184, 456, 1132, 2808, 6968, 17288, 42896, 106432, 264080, 655232, 1625760, 4033824, 10008704, 24833536, 61616832, 152883328, 379333248, 941199488, 2335298816, 5794330112, 14376858880, 35671780352, 88508618240 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

For n>=2, a(n)= Number of "stable LEGO walls" (i.e., walls in which seams don't match up from one level to the next) of width 7 and height n-1 when using bricks of length 2, 3, and 4. For example, there are a(2)=5 stable LEGO walls of height 1 and they are {[2,2,3],[2,3,2],[3,2,2],[3,4],[4,3]}. [From Emilie Hogan, Oct 16 2009]

LINKS

Table of n, a(n) for n=0..28.

S. Kitaev, J. Remmel, (a,b)-rectangle patterns in permutations and words, arXiv:1304.4286

FORMULA

Conjecture: a(n)=2*a(n-1)+2*a(n-2)-2*a(n-3) with g.f. (1-x^2)/(1-2*x-2*x^2+2*x^3). [From R. J. Mathar, Nov 10 2009]

CROSSREFS

Sequence in context: A046170 A262320 A062423 * A033482 A054341 A000106

Adjacent sequences:  A118646 A118647 A118648 * A118650 A118651 A118652

KEYWORD

nonn

AUTHOR

Joshua Zucker, May 10 2006

STATUS

approved

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Last modified October 21 06:44 EDT 2018. Contains 316405 sequences. (Running on oeis4.)