  The major semiaxes of the planets in our Solar System obey a simple geometric
progression known as the Titius-Bode Relation (TBR), whose physical origin
remains disputed. It has been shown that the exoplanetary systems follow a
similar (but not identical) progression of the form a_n= a_0 e^(bn), where a_0,
b are constants to be determined for each system. Since its formulation, the
Titius-Bode Relation has proved to be highly predictive in our Solar System.
Using data from 27 exoplanetary systems with 5 or more planets and applying a
proposed method, we conclude that reliable TB-like fits can be obtained for
systems with at least 4 planets and that the precision of the TBR is 78%. By
means of a statistical test we show that the periods of planets in real
exoplanetary systems are not consistent with a random distribution. Rather,
they show signs that their configuration is shaped by their mutual
interactions.
