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QuickStart Samples

# Prime Numbers QuickStart Sample (C#)

Illustrates working with prime numbers and the IntegerMath class in the Extreme.Mathematics namespace in C#.

```using System;

namespace Extreme.Numerics.QuickStart.CSharp
{
// We use many classes from the Extreme.Mathematics.SpecialFunctions
// namespace.
using Extreme.Mathematics;

/// <summary>
/// Illustrates working with prime numbers using the
/// IntegerMath class in the Extreme.Mathematics.SpecialFunctions
/// namespace of the Extreme Optimization Mathematics
/// Library for .NET.
/// </summary>
{
/// <summary>
/// The main entry point for the application.
/// </summary>
static void Main(string[] args)
{
//
// Factoring numbers
//

// The Factorize method returns an array containing the prime factors:
int index;

int n = 1001110110;
int[] factors = IntegerMath.Factorize(n);
Console.Write("{0} = {1}", n, factors[0]);
for(index = 1; index < factors.Length; index++)
Console.Write(" * {0}", factors[index]);
Console.WriteLine();

// Factors that occur multiple times is repeated as many times as necessary:
n = 256 * 6157413;
factors = IntegerMath.Factorize(n);
Console.Write("{0} = {1}", n, factors[0]);
for(index = 1; index < factors.Length; index++)
Console.Write(" * {0}", factors[index]);
Console.WriteLine();

// The 64bit version can safely factor numbers up to 48 bits long:
long n2 = 1296523 * 1177157L;
long[] factors2 = IntegerMath.Factorize(n2);
Console.Write("{0} = {1}", n2, factors2[0]);
for(index = 1; index < factors2.Length; index++)
Console.Write(" * {0}", factors2[index]);
Console.WriteLine();

//
// Prime numbers
//

// The IsPrime method verifies if a number is prime or not.
n = 801853937;
Console.WriteLine("{0} is prime? {1}!", n, IntegerMath.IsPrime(n));
n = 801853939;
Console.WriteLine("{0} is prime? {1}!", n, IntegerMath.IsPrime(n));

// MextPrime gets the first prime after a specified number.
// You can call it repeatedly to get successive primes.
// Let//s get the 10 smallest primes larger than one billion:
n = 1000000000;
Console.WriteLine("\nFirst 10 primes greater than 1 billion:");
for(index = 0; index < 10; index++)
{
n = IntegerMath.NextPrime(n);
Console.Write("{0,16}", n);
}
Console.WriteLine();

// PreviousPrime gets the last prime before a specified number.
n = 1000000000;
Console.WriteLine("Last 10 primes less than 1 billion:");
for(index = 0; index < 10; index++)
{
n = IntegerMath.PreviousPrime(n);
Console.Write("{0,16}", n);
}
Console.WriteLine();

Console.Write("Press Enter key to exit...");