' This method computes the list of prime numbers used by the
' IsPrime method.
Private Function BuildPrimeNumberList( _
    ByVal numberToTest As Integer, _
    ByVal asyncOp As AsyncOperation) As ArrayList

    Dim e As ProgressChangedEventArgs = Nothing
    Dim primes As New ArrayList
    Dim firstDivisor As Integer
    Dim n As Integer = 5

    ' Add the first prime numbers.
    primes.Add(2)
    primes.Add(3)

    ' Do the work.
    While n < numberToTest And _
        Not Me.TaskCanceled(asyncOp.UserSuppliedState)

        If IsPrime(primes, n, firstDivisor) Then
            ' Report to the client that you found a prime.
            e = New CalculatePrimeProgressChangedEventArgs( _
                n, _
                CSng(n) / CSng(numberToTest) * 100, _
                asyncOp.UserSuppliedState)

            asyncOp.Post(Me.onProgressReportDelegate, e)

            primes.Add(n)

            ' Yield the rest of this time slice.
            Thread.Sleep(0)
        End If

        ' Skip even numbers.
        n += 2

    End While

    Return primes

End Function

// This method computes the list of prime numbers used by the
// IsPrime method.
private ArrayList BuildPrimeNumberList(
    int numberToTest,
    AsyncOperation asyncOp)
{
    ProgressChangedEventArgs e = null;
    ArrayList primes = new ArrayList();
    int firstDivisor;
    int n = 5;

    // Add the first prime numbers.
    primes.Add(2);
    primes.Add(3);

    // Do the work.
    while (n < numberToTest && 
           !TaskCanceled( asyncOp.UserSuppliedState ) )
    {
        if (IsPrime(primes, n, out firstDivisor))
        {
            // Report to the client that a prime was found.
            e = new CalculatePrimeProgressChangedEventArgs(
                n,
                (int)((float)n / (float)numberToTest * 100),
                asyncOp.UserSuppliedState);

            asyncOp.Post(this.onProgressReportDelegate, e);

            primes.Add(n);

            // Yield the rest of this time slice.
            Thread.Sleep(0);
        }

        // Skip even numbers.
        n += 2;
    }

    return primes;
}