%I A054480
%S A054480 1,3,8,19,43,94,202,429,905,1901,3983,8332,17413,36370,75938,158519,
%T A054480 330862,690523,1441082,3007369,6275917,13096737,27330418,57033206,
%U A054480 119016808,248363751,518283950,1081551220,2256972626,4709831964
%N A054480 Number of different positive braids with n crossings of 4 strands.
%D A054480 P. Xu, Growth of the positive braids semigroups, Journal of Pure and 
               Applied Algebra, 1992.
%F A054480 G.f.: 1/(1-3x+x^2+2x^3-x^6)
%e A054480 a(3)=19 =#{111,112,113,121,122,123,132,133,211,213,221,222,223,232,233,
               321,322,332,333}
%Y A054480 Cf. A000071, A054761.
%Y A054480 Sequence in context: A161993 A008466 A102712 this_sequence A121551 A077850 
               A097550
%Y A054480 Adjacent sequences: A054477 A054478 A054479 this_sequence A054481 A054482 
               A054483
%K A054480 nonn,easy
%O A054480 0,2
%A A054480 Serge Burckel (burckel(AT)univ-reunion.fr), Apr 26 2000
%E A054480 More terms from Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 22 2002