  Here, we developed a complex network of solar active regions (ARs) to study
various local and global properties of the network. The values of the Hurst
exponent ($0.8-0.9$) were evaluated by both the detrended fluctuation analysis
and the rescaled range analysis applied on the time series of the AR numbers.
The findings suggest that ARs can be considered as a system of self-organized
criticality. We constructed a growing network based on locations, occurrence
times, and the lifetimes of 4,227 ARs recorded from 1 January 1999 to 14 April
2017. The behaviour of the clustering coefficient shows that the ARs network is
not a random network. The logarithmic behaviour of the length scale has the
characteristics of a so-called \textquotedblleft small-world
network\textquotedblright. It is found that the probability distribution of the
node degrees for undirected networks follows the power-law with exponents of
about 3.7 to 4.2. This indicates the scale-free nature of the ARs network. The
scale-free and small-world properties of the ARs network confirm that the
system of ARs forms a system of self-organized criticality. Our results show
that the occurrence probability of flares (classified by GOES class C $> 5$, M,
and X flares) in the position of the ARs network hubs take values greater than
that obtained for other nodes.
