The notation
is sometimes used to denote this function in number theoretic literature. However,
because Russian and German literature use the symbol to denote the base-10 logarithm and since this is the use
recommended by the United States Department of Commerce (Taylor 1995, p. 33),
this practice is discouraged. (To confuse matters even more, some German literature
uses the notation
to mean the binary logarithm.)

When information theoretic functions (like entropy) are computed using ,
the units of information are obtained in bits. When is used instead, the units of information are known
as "nats."

Taylor, B. N. Guide for the Use of the International System of Units (SI). United States Department of Commerce. NIST Special Publication
811, p. 33, 1995. http://physics.nist.gov/cuu/pdf/sp811.pdf.