Remove primes docs from rst, add a NEWS.md entry

Author: tkelman

NEWS.md

@@ -88,7 +88,7 @@ Breaking changes
 Library improvements
 --------------------
 
-  * Most of the  combinatorics functions have been moved from `Base`
+  * Most of the combinatorics functions have been moved from `Base`
     to the [Combinatorics.jl package](https://github.com/JuliaLang/Combinatorics.jl) ([#13897]).
 
   * Packages:
@@ -165,6 +165,9 @@ Library improvements
   * The `libjulia` library is now properly versioned and installed to the public `<prefix>/lib`
     directory, instead of the private `<prefix>/lib/julia` directory.
 
+  * Prime number related functions have been moved from `Base` to the
+    [Primes.jl package](https://github.com/JuliaMath/Primes.jl) ([#16481]).
+
 Deprecated or removed
 ---------------------
 

doc/stdlib/math.rst

@@ -1359,19 +1359,6 @@ Mathematical Functions
 
    Compute ``factorial(n)/factorial(k)``\ .
 
-.. function:: factor(n) -> Dict
-
-   .. Docstring generated from Julia source
-
-   Compute the prime factorization of an integer ``n``\ . Returns a dictionary. The keys of the dictionary correspond to the factors, and hence are of the same type as ``n``\ . The value associated with each key indicates the number of times the factor appears in the factorization.
-
-   .. doctest::
-
-       julia> factor(100) # == 2*2*5*5
-       Dict{Int64,Int64} with 2 entries:
-         2 => 2
-         5 => 2
-
 .. function:: gcd(x,y)
 
    .. Docstring generated from Julia source

doc/stdlib/numbers.rst

@@ -455,40 +455,6 @@ Integers
        julia> trailing_ones(3)
        2
 
-.. function:: isprime(x::Integer) -> Bool
-
-   .. Docstring generated from Julia source
-
-   Returns ``true`` if ``x`` is prime, and ``false`` otherwise.
-
-   .. doctest::
-
-       julia> isprime(3)
-       true
-
-.. function:: isprime(x::BigInt, [reps = 25]) -> Bool
-
-   .. Docstring generated from Julia source
-
-   Probabilistic primality test. Returns ``true`` if ``x`` is prime; and ``false`` if ``x`` is not prime with high probability. The false positive rate is about ``0.25^reps``\ . ``reps = 25`` is considered safe for cryptographic applications (Knuth, Seminumerical Algorithms).
-
-   .. doctest::
-
-       julia> isprime(big(3))
-       true
-
-.. function:: primes([lo,] hi)
-
-   .. Docstring generated from Julia source
-
-   Returns a collection of the prime numbers (from ``lo``\ , if specified) up to ``hi``\ .
-
-.. function:: primesmask([lo,] hi)
-
-   .. Docstring generated from Julia source
-
-   Returns a prime sieve, as a ``BitArray``\ , of the positive integers (from ``lo``\ , if specified) up to ``hi``\ . Useful when working with either primes or composite numbers.
-
 .. function:: isodd(x::Integer) -> Bool
 
    .. Docstring generated from Julia source