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%I #11 Sep 02 2019 05:23:44
%S 1,1,2,7,36,265,3039,56532,1795771,100752242,10189358360,
%T 1879720735880,637617233537026,400169631647375590,
%U 467115844246503901102,1018822456144128438039598,4169121243929999956903622399,32126195519194538601647462868271
%N Number of unlabeled connected bicolored graphs on 2n nodes which are invariant when the two color classes are interchanged.
%D R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.
%F a(n) = 2*A005142(2*n) - A318870(2*n). - _Andrew Howroyd_, Sep 04 2018
%t A005142 = Import["https://oeis.org/A005142/b005142.txt", "Table"][[All, 2]];
%t A318870 = Import["https://oeis.org/A318870/b318870.txt", "Table"][[All, 2]];
%t a[n_] := 2*A005142[[2*n + 1]] - A318870[[2*n + 1]];
%t a /@ Range[0, 17] (* _Jean-François Alcover_, Sep 02 2019 *)
%Y Row sums of A123550.
%Y Cf. A005142, A318869, A318870.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Nov 14 2006
%E a(0)=1 prepended and terms a(8) and beyond from _Andrew Howroyd_, Sep 04 2018
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