Class groups of quadratic fields. II

A computation has been made of the noncyclic class groups of imaginary quadratic fields $Q(\sqrt { - D} )$ for even and odd discriminants $- D$ from 0 to $- 25000000$. Among the results are that 95% of the class groups are cyclic, and that $- 11203620$ and $- 18397407$ are the first discriminants of imaginary quadratic fields for which the class group has rank three in the 5-Sylow subgroup. The latter was known to be of rank three; this computation demonstrates that it is the first odd discriminant of 5-rank three or more.