The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ?

Prime factors are prime numbers that can be multiplied together to make a given number. One way to find them is to start by dividing the number by the first prime (2) and continuing to do so until it cannot be divided, then moving on to the next.

Module Module1 Sub Main() Dim beganAt As Date = Now Dim n As Long = 600851475143 Dim factor As Integer = 2 Dim highestFactor As Integer = 1 While n > 1 If n Mod factor = 0 Then highestFactor = factor n = n / factor While n Mod factor = 0 n = n / factor End While End If factor = factor + 1 End While Dim endAt As Global.System.TimeSpan = Now.Subtract(beganAt) Dim took As Integer = endAt.Milliseconds Console.WriteLine(highestFactor.ToString + " in " + took.ToString + "ms.") Console.ReadKey() End Sub End Module