The Buchstab function 
is defined by the delay differential equation
 |
(1)
|
(Panario 1998). It approaches the asymptotic value 
as 
, where 
is the Euler-Mascheroni
constant. It has nearly reached this value already by 
.
For 
, let 
be the number of positive
integers 
whose prime divisors all exceed 
. Then
 |
(2)
|
as 
(Drappeau and Mounier 2026).
