More generally, every finitely generated Abelian group is isomorphic to the group direct sum of a finite
number of groups, each of which is either cyclic of prime
power order or isomorphic to . This extension of Kronecker decomposition theorem is often
referred to as the Kronecker basis theorem.

Kargapolov, M. I. and Merzljako, Ju. I. Fundamentals
of the Theory of Groups. New York: Springer-Verlag, p. 55, 1979.Schenkman,
E. Group
Theory. Princeton, NJ: Van Nostrand, p. 48, 1965.Sloane,
N. J. A. Sequence A000688/M0064
in "The On-Line Encyclopedia of Integer Sequences."