A natural number of the form
where the are prime numbers and is a constant. Prime numbers are the special case of almost-prime numbers for . There are theorems for almost-prime numbers that generalize theorems on the distribution of prime numbers in the set of natural numbers. Several additive problems that have not yet been solved for prime numbers have been solved for almost-prime numbers.
See also Sieve method.
An example of a result on the distribution of almost-prime numbers generalizing the corresponding one on prime numbers is the following. Let be the number of square-free almost-prime numbers . Then (cf. [a1], Sect. 22.18)
|[a1]||G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Clarendon Press (1965)|
Almost-prime number. B.M. Bredikhin (originator), Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Almost-prime_number&oldid=12988