%I #4 Mar 30 2012 17:36:31
%S 1,1,1,2,1,1,3,3,2,1,8,5,4,2,1,16,13,9,6,3,1,41,28,21,13,8,3,1,98,71,
%T 49,33,20,10,4,1,250,174,121,79,50,27,13,4,1,631,445,304,201,127,74,
%U 38,16,5,1,1646,1137,776,510,325,192,106,49,19,5,1,4285,2974
%N Triangle T(n,k) (n >= 1, k >= 1) giving filtration of bigrading of Hopf algebra of rooted trees.
%H D. J. Broadhurst and D. Kreimer, <a href="http://arXiv.org/abs/hep-th/0001202">Towards cohomology of renormalization...</a>
%e 1; 1,1; 2,1,1; 3,3,2,1; 8,5,4,2,1; ...
%Y Cf. A052250.
%K nonn,nice,tabl
%O 0,4
%A _David Broadhurst_, Feb 05 2000