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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]}. [Emilie Hogan, Oct 16 2009] LINKS S. Kitaev and J. Remmel, (a,b)-rectangle patterns in permutations and words, arXiv:1304.4286 [math.CO], 2013. 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). [R. J. Mathar, Nov 10 2009] MATHEMATICA Total[CoefficientList[#, y]]& /@ CoefficientList[(1 - x^2 y)/(1 - x - x y - 2 x^2 y + x^3 y + x^3 y^2) + O[x]^29, x] (* Jean-François Alcover, Oct 30 2018, after Emanuele Munarini in A106597 *) CROSSREFS Cf. A106597. 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 September 28 10:48 EDT 2021. Contains 347714 sequences. (Running on oeis4.)