

A187928


Number of embeddings on the sphere of 2connected planar graphs, minimum vertex degree 3, with n edges.


1



1, 1, 4, 15, 42, 135, 440, 1480, 5106, 17890, 63264, 226018, 812354, 2936837, 10666188, 38901190, 142386358
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

10,3


COMMENTS

The graphs are exactly 2connected, not at least 2connected. The graphs were enumerated using plantri (by B.D. McKay & G. Brinkmann) for the purpose of finding compound perfect squared squares. If all graphs with n edges are generated then all compound squares in order n1 can be obtained from them. Graphs with minimum degree 3 are also called homeomorphically irreducible.


LINKS

Table of n, a(n) for n=10..26.
Stuart Anderson, Compound Perfect Squared Squares
B. D. McKay and G. Brinkmann, Plantri Guide
Gunnar Brinkmann and Brendan McKay, Guide to using plantri [Cached copy, with permission]


PROG

use;
plantri p c2 m3 e# x u v n ; or
plantri pc2m3e#xuv n
to count graphs by node number (n) and edge number (#)


CROSSREFS

Cf. A034889, A181340, A187927, A021103.
Sequence in context: A100503 A085829 A085567 * A213498 A294259 A240359
Adjacent sequences: A187925 A187926 A187927 * A187929 A187930 A187931


KEYWORD

nonn,more,hard


AUTHOR

Stuart E Anderson, Mar 16 2011


EXTENSIONS

Corrected a(22)  Stuart E Anderson, Feb 24 2013
a(23)a(26) from Lorenz Milla, Oct 08 2013


STATUS

approved



