The graph corona product, also called the corona of graphs 
and 
, is the graph 
formed from one copy of 
and one copy 
of 
for each vertex 
of 
by joining 
to every vertex of 
. The operation was introduced by Frucht and Harary (1970).
If 
has vertex count 
and edge count 
, while 
has vertex count 
and edge count 
, then
 |
and
 |
Each vertex 
in the original copy of 
has vertex degree 
, while a vertex 
in 
has vertex degree 
. The chromatic
number is 
.
The vertex count formula shows that the graph corona product is in general neither commutative nor associative.
The following table gives some common special cases, where 
is the empty graph on 
vertices.
| product | result |
 | graph join  |
 | complete
graph  |
 | wheel
graph  |
 | star
graph  |
 |  -centipede graph |
 |  -sunlet graph |
The sunlet graph is also called an "
-sun graph" by some authors,
although that name is also commonly used for a different graph.
