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


IsPrime[n_Integer] := Block[{},
  If[n <= 1, Return[False]];
  If[n == 2, Return[True]]; If[Mod[n, 2] == 0, Return[False]];
  For[k = 3, k <= Sqrt[n], k += 2, If[Mod[n, k] == 0, Return[False]]];
  Return[True]]