Search: id:A118649
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%I A118649
%S A118649 1,2,5,12,30,74,184,456,1132,2808,6968,17288,42896,106432,264080,655232,
%T A118649 1625760,4033824,10008704,24833536,61616832,152883328,379333248,
%U A118649 941199488,2335298816,5794330112,14376858880,35671780352,88508618240
%N A118649 Row sums for A106597.
%C A118649 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 (eahogan(AT)math.rutgers.edu), 
               Oct 16 2009]
%F A118649 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 (mathar(AT)strw.leidenuniv.nl), Nov 10 2009]
%Y A118649 Sequence in context: A157748 A046170 A062423 this_sequence A033482 A054341 
               A000106
%Y A118649 Adjacent sequences: A118646 A118647 A118648 this_sequence A118650 A118651 
               A118652
%K A118649 nonn
%O A118649 0,2
%A A118649 Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), May 10 2006

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