Difference between revisions of "Almost-prime number"
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| − | + | A natural number $ n $ | |
| + | of the form | ||
| + | $$ | ||
| + | n = p _ {1} \dots p _ {k} , | ||
| + | $$ | ||
| + | where the $ p _ {i} $ | ||
| + | are prime numbers and $ k \geq 1 $ | ||
| + | is a constant. Prime numbers are the special case of almost-prime numbers for $ k = 1 $. | ||
| + | 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|additive problems]] that have not yet been solved for prime numbers have been solved for almost-prime numbers. | ||
====Comments==== | ====Comments==== | ||
See also [[Sieve method|Sieve method]]. | See also [[Sieve method|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 | + | An example of a result on the distribution of almost-prime numbers generalizing the corresponding one on prime numbers is the following. Let $ \pi _ {k} (x) $ |
| + | be the number of square-free almost-prime numbers $ \leq x $. | ||
| + | Then (cf. [[#References|[a1]]], Sect. 22.18) | ||
| − | + | $$ | |
| + | \pi _ {k} (x) \sim \ | ||
| + | |||
| + | \frac{x ( { \mathop{\rm log} \mathop{\rm log} } x ) ^ {k-1} }{( k - 1 ) ! \mathop{\rm log} x } | ||
| + | . | ||
| + | $$ | ||
====References==== | ====References==== | ||
<table><TR><TD valign="top">[a1]</TD> <TD valign="top"> G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Clarendon Press (1965)</TD></TR></table> | <table><TR><TD valign="top">[a1]</TD> <TD valign="top"> G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Clarendon Press (1965)</TD></TR></table> | ||
Latest revision as of 16:10, 1 April 2020
A natural number $ n $
of the form
$$ n = p _ {1} \dots p _ {k} , $$
where the $ p _ {i} $ are prime numbers and $ k \geq 1 $ is a constant. Prime numbers are the special case of almost-prime numbers for $ k = 1 $. 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.
Comments
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 $ \pi _ {k} (x) $ be the number of square-free almost-prime numbers $ \leq x $. Then (cf. [a1], Sect. 22.18)
$$ \pi _ {k} (x) \sim \ \frac{x ( { \mathop{\rm log} \mathop{\rm log} } x ) ^ {k-1} }{( k - 1 ) ! \mathop{\rm log} x } . $$
References
| [a1] | G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Clarendon Press (1965) |
How to Cite This Entry:
Almost-prime number. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Almost-prime_number&oldid=12988
Almost-prime number. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Almost-prime_number&oldid=12988
This article was adapted from an original article by B.M. Bredikhin (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article