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%I #18 Nov 10 2019 01:39:20
%S 0,0,0,0,3,16,112,927,11995,273438,12000099,1018972683,165091020547,
%T 50502030251549,29054155647335623,31426485969699328399,
%U 64001015704526239877379,245935864153532913256188013,1787577725145611700213913518632,24637809253125004524376347209365832
%N Number of n-node graphs containing a 4-cycle.
%D F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 228.
%F a(n) = A000088(n) - A006786(n). - _Falk Hüffner_, Nov 27 2015
%t A000088 = Cases[Import["https://oeis.org/A000088/b000088.txt", "Table"], {_, _}][[All, 2]];
%t A006786 = Cases[Import["https://oeis.org/A006786/b006786.txt", "Table"], {_, _}][[All, 2]];
%t a[n_] := If[n < 2, 0, A000088[[n + 1]] - A006786[[n]]];
%t a /@ Range[0, 19] (* _Jean-François Alcover_, Nov 10 2019 *)
%K nonn,nice
%O 0,5
%A _N. J. A. Sloane_
%E Using formula, a(0) and a(6) corrected and more terms added by _Falk Hüffner_, Nov 27 2015
%E a(18)-a(19) from A000088 and A006786 by _Jean-François Alcover_, Nov 10 2019
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