A006403 Number of unsensed 2-connected planar maps with n edges.

0, 1, 2, 3, 6, 15, 36, 114, 396, 1565, 6756, 31563, 154370, 785113, 4099948, 21870704, 118624544, 652485364, 3631820462, 20426666644, 115949791342, 663640383400, 3826858500878, 22218232389849, 129802836253994

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

The maps considered here may include parallel edges. - Andrew Howroyd, Jan 13 2025

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
• Timothy R. Walsh, personal communication.

Links

• Timothy R. Walsh, Generating nonisomorphic maps without storing them, SIAM J. Algebraic Discrete Methods 4 (1983), no. 2, 161-178.
• Timothy R. Walsh, Number of sensed planar maps with n edges and m vertices, p. 41.

Crossrefs

Row sums of A379432.

Cf. A000139 (rooted), A006385, A006402 (sensed), A006407 (without parallel edges), A006444 (achiral).

Formula

a(n) = (A006402(n) + A006444(n))/2. - Andrew Howroyd, Jan 13 2025

Extensions

a(23)-a(25) added by Andrew Howroyd, Jan 13 2025