A007164 Number of P-graphs with 2n edges.

1, 2, 7, 31, 167, 999, 6495, 44619, 319463, 2356406, 17775821, 136405506, 1060866006, 8339982193, 66147792753, 528559162227, 4250413757583, 34368723106860, 279254390054538, 2278795583070154, 18667432144042678, 153452484745198722

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

References

• R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math., 31 (1986), 47-63.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A003169, A007163, A007165.

Formula

a(n) = (A003169(n) + 2 * A007165(n) + A007163(n)) / 4. - Sean A. Irvine, Nov 06 2017

Extensions

a(5), a(9), a(10) corrected and more terms from Sean A. Irvine, Nov 06 2017