In mathematics, the Feller–Tornier constant CFT is the density of the set of all positive integers that have an even number of distinct prime factors raised to a power larger than one (ignoring any prime factors which appear only to the first power).
[1] It is named after William Feller (1906–1970) and Erhard Tornier (1894–1982)[2] (sequence A065493 in the OEIS) The Big Omega function is given by See also: Prime omega function.
The Iverson bracket is With these notations, we have The prime zeta function P is give by The Feller–Tornier constant satisfies