The construction number of a graph
with vertex set
and edge set
is the number of distinct construction sequences for
(Kainen 2023). For the graph
, a construction sequence, or c-sequence, for
is a linear order on
in which each edge appears after both of its endpoints.
For example, for the path graph with vertex set 1, 2, 3 and
edge set 12, 23, there are a total of 16 possible construction
sequences: (1, 2, 3, 12, 23), (1, 2, 3, 23, 12), (1, 2, 12, 3, 23), (1, 3, 2, 12,
23), (1, 3, 2, 23, 12), (2, 1, 3, 12, 23), (2, 1, 3, 23, 12), (2, 1, 12, 3, 23),
(2, 3, 1, 12, 23), (2, 3, 1, 23, 12), (2, 3, 23, 1, 12), (3, 1, 2, 12, 23), (3, 1,
2, 23, 12), (3, 2, 1, 12, 23), (3, 2, 1, 23, 12), (3, 2, 23, 1, 12), giving
.
The construction numbers for a number of parametrized graph are summarized in the table below (cf. Kainen 2023), where is the binomial coefficient,
is a factorial,
is a double factorial,
is a Bernoulli number, and
is the gamma function.
The determination of
was proposed by Kainen et al. (2023) and solved
by Tauraso (2024).
| family | OEIS | construction number |
| complete
graph | A374928 | |
| cycle graph | A024255 | |
| empty graph | A000142 | |
| ladder rung graph | A210277 | |
| path graph | A000182 | |
| star graph | A055546 |