A 
-rough number is a positive
integer all of whose prime factors are greater
than or equal to 
(Finch 2001).
Greene and Knuth (1990) define "unusual numbers" as positive integers 
whose greatest prime factor is greater than
or equal to 
.
This condition differs from being 
-rough, which for 
requires 
to be a prime number or 
for a prime
number 
.
For example, 6 is unusual but is not 
-rough. The first few unusual numbers are 2, 3, 4, 5,
6, 7, 9, 10, 11, 13, ... (OEIS A063538), which
turn out to not be so unusual after all (Greene and Knuth 1990, Finch 2001). Including
1 by convention, the first few "usual" numbers are 1, 8, 12, 16, 18, 24,
27, 30, ... (OEIS A063539).
Finch (2003, p. 166) calls 
jagged when its greatest
prime factor is strictly greater than 
. These numbers differ from unusual numbers by excluding
numbers 
with 
prime.
For an integer sampled uniformly from 1, 2, ..., 
, the probability of obtaining 
whose greatest prime
factor exceeds 
tends to 
as 
(Schroeppel 1972).
