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%I #12 Apr 03 2023 09:29:41
%S 1,4,96,10240,4587520,8455716864,63496796504064,1932044240141942784,
%T 237409596228641929297920,117555946699326540948428554240,
%U 234206054295766751302924897412448256,1875359927045089548108556844295368069873664
%N Number of labeled graphs having n blue nodes and n green ones, where edges join only nodes of different colors.
%D H. S. Wilf, Generatingfunctionology, 2nd edn., Academic Press, NY, 1994, p. 88.
%F a(n) = C(2n,n) * 2^(n^2).
%F a(n) = A000984(n) * A002416(n).
%F a(n) = A111636(2n,n).
%e a(1) = 4 because we have B G, B--G, G B and G--B, where B (G) stands for a blue (green) node and -- denotes an edge.
%p a:= n-> 2^(n^2)*binomial(2*n,n): seq(a(n),n=0..12);
%Y Cf. A111636, A000984, A002416.
%K nonn
%O 0,2
%A _Emeric Deutsch_, Aug 09 2005