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A123550 Triangle read by rows: T(n,k) = number of unlabeled connected bicolored graphs having 2n nodes and k edges, which are invariant when the two color classes are interchanged. Here n >= 0, 0 <= k <= n^2.

%I A123550 #4 Mar 30 2012 16:50:35
%S A123550 0,1,0,0,0,1,1,0,0,0,0,0,2,2,1,1,1,0,0,0,0,0,0,0,4,6,6,6,5,4,2,1,1,1,
%T A123550 0,0,0,0,0,0,0,0,0,9,15,23,31,36,34,31,27,21,14,9,6,4,2,1,1,1,0,0,0,0,
%U A123550 0,0,0,0,0,0,0,20,44,84,134,196,249,288,313,317,303,267,224,180
%N A123550 Triangle read by rows: T(n,k) = number of unlabeled connected bicolored graphs having 2n nodes and k edges, which are invariant when the two color classes are interchanged. Here n >= 0, 0 <= k <= n^2.
%D A123550 R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.
%H A123550 R. W. Robinson, <a href="/A123550/b123550.txt">Rows 0 through 7, flattened</a>
%e A123550 Triangle begins:
%e A123550 n = 1
%e A123550 k = 0 : 0
%e A123550 k = 1 : 1
%e A123550 Total = 1
%e A123550 n = 2
%e A123550 k = 0 : 0
%e A123550 k = 1 : 0
%e A123550 k = 2 : 0
%e A123550 k = 3 : 1
%e A123550 k = 4 : 1
%e A123550 Total = 2
%e A123550 n = 3
%e A123550 k = 0 : 0
%e A123550 k = 1 : 0
%e A123550 k = 2 : 0
%e A123550 k = 3 : 0
%e A123550 k = 4 : 0
%e A123550 k = 5 : 2
%e A123550 k = 6 : 2
%e A123550 k = 7 : 1
%e A123550 k = 8 : 1
%e A123550 k = 9 : 1
%e A123550 Total = 7
%K A123550 nonn,tabf
%O A123550 1,13
%A A123550 _N. J. A. Sloane_, Nov 14 2006