Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


open NUnit.Framework
open FsUnit
let inline isPrime n = not ({uint64 2..uint64 (sqrt (double n))} |> Seq.exists (fun (i:uint64) -> uint64 n % i = uint64 0))
[<Test>]
let ``Validate that 2 is prime`` () =
  isPrime 2 |> should equal true
 
[<Test>]
let ``Validate that 4 is not prime`` () =
  isPrime 4 |> should equal false
 
[<Test>]
let ``Validate that 3 is prime`` () =
  isPrime 3 |> should equal true
 
[<Test>]
let ``Validate that 9 is not prime`` () =
  isPrime 9 |> should equal false
 
[<Test>]
let ``Validate that 5 is prime`` () =
  isPrime 5 |> should equal true
 
[<Test>]
let ``Validate that 277 is prime`` () =
  isPrime 277 |> should equal true