A039751 Number of n-node graphs containing a 4-cycle.

0, 0, 0, 0, 3, 16, 112, 927, 11995, 273438, 12000099, 1018972683, 165091020547, 50502030251549, 29054155647335623, 31426485969699328399, 64001015704526239877379, 245935864153532913256188013, 1787577725145611700213913518632, 24637809253125004524376347209365832

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• nice

References

• F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 228.

Programs

Mathematica

A000088 = Cases[Import["https://oeis.org/A000088/b000088.txt", "Table"], {, }][[All, 2]];
A006786 = Cases[Import["https://oeis.org/A006786/b006786.txt", "Table"], {, }][[All, 2]];
a[n_] := If[n < 2, 0, A000088[[n + 1]] - A006786[[n]]];
a /@ Range[0, 19] (* Jean-François Alcover, Nov 10 2019 *)

Formula

a(n) = A000088(n) - A006786(n). - Falk Hüffner, Nov 27 2015

Extensions

Using formula, a(0) and a(6) corrected and more terms added by Falk Hüffner, Nov 27 2015

a(18)-a(19) from A000088 and A006786 by Jean-François Alcover, Nov 10 2019