

A245246


Number of ways to delete an edge (up to the outcome) in the simple unlabeled graphs on n nodes.


2




OFFSET

1,3


COMMENTS

Also, the number of distinct pairs (G,H) of simple unlabeled graphs on n nodes, where H can be obtained from G by deletion of a single edge.
For n<6, we have a(n) = A126122(n), since the nonisomorphic edges in a graph on n<6 nodes uniquely define the result of their deletion. However, there is a graph on 6 nodes (see link below) with two nonisomorphic edges, deletion of either of which results in the same graph. Hence, for n>=6, a(n) < A126122(n).


LINKS

Table of n, a(n) for n=1..9.
Max Alekseyev, Example of the graph on 6 nodes, where deletion of red or blue edge (which are nonisomorphic) results in the same graph.
Max Alekseyev et al., Removal of nonisomorphic edges results in the same graph, MathOverflow, 2014.


CROSSREFS

Cf. A000088, A126122
Sequence in context: A277939 A210346 A074549 * A126122 A303034 A026004
Adjacent sequences: A245243 A245244 A245245 * A245247 A245248 A245249


KEYWORD

nonn,more


AUTHOR

Max Alekseyev, Jul 15 2014


STATUS

approved



