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%I #4 Sep 21 2013 12:51:42
%S 9,0,27,0,9,72,0,0,69,174
%N Triangle T(n,k) (n >= 2, 1 <= k <= n-1) read by rows, where T(n,k) is the number of words of length n in the free group on three generators that require exactly k multiplications for their formation.
%e T(4,2)= 9 because each of aaaa,bbbb,cccc,abab,acac,baba,bcbc,caca,cbcb can be formed in just two multiplications: e.g. ab=a*b, abab=ab*ab.
%Y Cf. A076261.
%K more,nonn,tabl
%O 2,1
%A _Colin Mallows_, Oct 03 2002
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