Generate Primes over 100 Million

[patplays852]

Hello, I salvaged the following piece of code from:
http://www.vbforums.com/showpost.php...65&postcount=8

This code works fine, but the problem comes when I need to get all the primes above 100 million. I am familar (at least a little bit) with the BigInteger class in .NET 4.0, but when I replace all the instances of "Integer" with "BigInteger" in the following code I get this error:
Value of type 'System.Collections.Generic.List(Of System.Numerics.BigInteger)' cannot be converted to 'System.Collections.Generic.List(Of Integer)'.

(The reason I need primes above 100 million is that I'm trying to work through some projects on www.projecteuler.net)

Anyone have some ideas on how to modify the code to work with BigIntegers, Thank you very much for your help. If you need more code examples please ask.

'Sieve of Eratosthenes 
    'http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes 
    '1. Create a contiguous list of numbers from two to some highest number n. 
    '2. Strike out from the list all multiples of two (4, 6, 8 etc.). 
    '3. The list's next number that has not been struck out is a prime number. 
    '4. Strike out from the list all multiples of the number you identified in the previous step. 
    '5. Repeat steps 3 and 4 until you reach a number that is greater than the square root of n (the highest number in the list). 
    '6. All the remaining numbers in the list are prime. 
    Private Function Sieve_of_Eratosthenes(ByVal MaxNum As Integer) As List(Of Integer)
        'tested to MaxNum = 10,000,000 - on 1.8Ghz Laptop it took 1.4 seconds
        Dim thePrimes As New List(Of Integer)
        Dim toNum As Integer = MaxNum, stpw As New Stopwatch
        If toNum > 1 Then 'the first prime is 2
            stpw.Start()
            thePrimes.Capacity = toNum 'size the list
            Dim idx As Integer
            Dim stopAT As Integer = CInt(Math.Sqrt(toNum) + 1)
            '1. Create a contiguous list of numbers from two to some highest number n.
            '2. Strike out from the list all multiples of 2, 3, 5. 
            For idx = 0 To toNum
                If idx > 5 Then
                    If idx Mod 2 <> 0 _
                    AndAlso idx Mod 3 <> 0 _
                    AndAlso idx Mod 5 <> 0 Then thePrimes.Add(idx) Else thePrimes.Add(-1)
                Else
                    thePrimes.Add(idx)
                End If
            Next
            'mark 0,1 and 4 as non-prime
            thePrimes(0) = -1
            thePrimes(1) = -1
            thePrimes(4) = -1
            Dim aPrime, startAT As Integer
            idx = 7 'starting at 7 check for primes and multiples 
            Do
                '3. The list's next number that has not been struck out is a prime number. 
                '4. Strike out from the list all multiples of the number you identified in the previous step. 
                '5. Repeat steps 3 and 4 until you reach a number that is greater than the square root of n (the highest number in the list). 
                If thePrimes(idx) <> -1 Then ' if equal to -1 the number is not a prime
                    'not equal to -1 the number is a prime
                    aPrime = thePrimes(idx)
                    'get rid of multiples 
                    startAT = aPrime * aPrime
                    For mltpl As Integer = startAT To thePrimes.Count - 1 Step aPrime
                        If thePrimes(mltpl) <> -1 Then thePrimes(mltpl) = -1
                    Next
                End If
                idx += 2 'increment index 
            Loop While idx < stopAT
            '6. All the remaining numbers in the list are prime. 
            thePrimes = thePrimes.FindAll(Function(i As Integer) i <> -1)
            stpw.Stop()
            Debug.WriteLine(stpw.ElapsedMilliseconds)
        End If
        Return thePrimes
    End Function

And here is what I changed it to:

Private Function Sieve_of_Eratosthenes(ByVal MaxNum As BigInteger) As List(Of BigInteger)
          'tested to MaxNum = 10,000,000 - on 1.8Ghz Laptop it took 1.4 seconds
          Dim thePrimes As New List(Of BigInteger)
          Dim toNum As BigInteger = MaxNum, stpw As New Stopwatch
          If toNum > 1 Then 'the first prime is 2
               stpw.Start()
               thePrimes.Capacity = toNum 'size the list
               Dim idx As BigInteger
               Dim stopAT As BigInteger = Math.Sqrt(toNum) + 1
               '1. Create a contiguous list of numbers from two to some highest number n.
               '2. Strike out from the list all multiples of 2, 3, 5. 
               For idx = 0 To toNum
                    If idx > 5 Then
                         If idx Mod 2 <> 0 _
                         AndAlso idx Mod 3 <> 0 _
                         AndAlso idx Mod 5 <> 0 Then thePrimes.Add(idx) Else thePrimes.Add(-1)
                    Else
                         thePrimes.Add(idx)
                    End If
               Next
               'mark 0,1 and 4 as non-prime
               thePrimes(0) = -1
               thePrimes(1) = -1
               thePrimes(4) = -1
               Dim aPrime, startAT As BigInteger
               idx = 7 'starting at 7 check for primes and multiples 
 
               Do
                    '3. The list's next number that has not been struck out is a prime number. 
                    '4. Strike out from the list all multiples of the number you identified in the previous step. 
                    '5. Repeat steps 3 and 4 until you reach a number that is greater than the square root of n (the highest number in the list). 
                    If thePrimes(idx) <> -1 Then ' if equal to -1 the number is not a prime
                         'not equal to -1 the number is a prime
                         aPrime = thePrimes(idx)
                         'get rid of multiples 
                         startAT = aPrime * aPrime
                         For mltpl As BigInteger = startAT To thePrimes.Count - 1 Step aPrime
                              If thePrimes(mltpl) <> -1 Then thePrimes(mltpl) = -1
                         Next
                    End If
                    idx += 2 'increment index 
               Loop While idx < stopAT
 
               '6. All the remaining numbers in the list are prime. 
               thePrimes = thePrimes.FindAll(Function(i As BigInteger) i <> -1)
               stpw.Stop()
               Console.WriteLine(stpw.ElapsedMilliseconds & " milliseconds to generate primes")
          End If
          Return thePrimes
     End Function