Let be a complex number, then inequality
(1)

holds in the lensshaped region illustrated above. Written explicitly in terms of real variables, this can be written as
(2)

where
(3)

The area enclosed is roughly
(4)

(OEIS A140133).
This region can be parameterized in terms of a variable as
(5)
 
(6)

Written parametrically in terms of the Cartesian coordinates,
(7)
 
(8)

This region is intimately related to the study of Bessel functions and Kapteyn series (Plummer 1960, p. 47; Watson 1966, p. 270).
reaches its maximum value at (OEIS A085984; Goursat 1959, p. 120; Le Lionnais 1983, p. 36), given by the root of
(9)

or equivalently by the root of
(10)

as noted by Stieltjes.
The minimum value of corresponding to the maximum value is (OEIS A033259; Plummer 1960, p. 47; Watson 1966, p. 270), which is known as the Laplace limit constant. It is precisely the point at which Laplace's formula for solving Kepler's equation begins diverging, and is given by the unique real solution of for
(11)

The continued fraction of is given by [0, 1, 1, 1, 27, 1, 1, 1, 8, 2, 154, ...] (OEIS A033260). The positions of the first occurrences of in the continued fraction of are 2, 10, 35, 13, 15, 32, 101, 9, ... (OEIS A033261). The incrementally largest terms in the continued fraction are 1, 27, 154, 1601, 2135, ... (OEIS A033262), which occur at positions 2, 5, 11, 19, 1801, ... (OEIS A033263).