Omega constant

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The omega constant is a mathematical constant defined as the unique real number that satisfies the equation

It is the value of W(1), where W is Lambert's W function. The name is derived[citation needed] from the alternate name for Lambert's W function, the omega function. The numerical value of Ω is given by

Ω = 0.567143290409783872999968662210... (sequence A030178 in the OEIS).
1/Ω = 1.763222834351896710225201776951... (sequence A030797 in the OEIS).


Fixed point representation[edit]

The defining identity can be expressed, for example, as




One can calculate Ω iteratively, by starting with an initial guess Ω0, and considering the sequence

This sequence will converge to Ω as n approaches infinity. This is because Ω is an attractive fixed point of the function ex.

It is much more efficient to use the iteration

because the function

in addition to having the same fixed point, also has a derivative that vanishes there. This guarantees quadratic convergence; that is, the number of correct digits is roughly doubled with each iteration.

Using Halley's method, Ω can be approximated with cubic convergence (the number of correct digits is roughly tripled with each iteration): (see also Lambert W function § Numerical evaluation).

Integral representations[edit]

An identity due to Victor Adamchik[citation needed] is given by the relationship

Another relations due to I. Mező are[1][2]

The latter two identities can be extended to other values of the W function (see also Lambert W function § Representations).


The constant Ω is transcendental. This can be seen as a direct consequence of the Lindemann–Weierstrass theorem. For a contradiction, suppose that Ω is algebraic. By the theorem, e−Ω is transcendental, but Ω = e−Ω, which is a contradiction. Therefore, it must be transcendental.


  1. ^ István, Mező. "An integral representation for the principal branch of Lambert the W function". Archived from the original on 28 December 2016. Retrieved 7 November 2017.
  2. ^ Mező, István (2020). "An integral representation for the Lambert W function". arXiv:2012.02480 [math.CA]..

External links[edit]