An equation proposed by Lambert (1758) and studied by Euler in 1779 (Euler 1921).
References
de Bruijn, N. G. Asymptotic Methods in Analysis. Amsterdam, Netherlands: North-Holland, pp. 27-28, 1961.
Euler, L. ``De Serie Lambertina Plurismique Eius Insignibus Proprietatibus.'' Leonhardi Euleri Opera
Omnia, Ser. 1. Opera Mathematica, Bd. 6, 1921.
Lambert, J. H. ``Observations variae in Mathesin Puram.'' Acta Helvitica,
physico-mathematico-anatomico-botanico-medica 3, 128-168, 1758.