Function esPrimo( Integer sNum ) return Boolean
   Integer sCont = 0
   For i = 0 To sNum
    If (sNum MOD i == 0) Then
      sCont = sCont + 1
    End If
   Next
 
  If ( sCont == 2 ) Then
    Return true
  Else
    Return false
  End If
End Function

  Integer sMen = 3, sMax = 50
 
  For i = sMen To sMax
    If ( esPrimo( i )  == true ) Then
      Print i
    End If
  Next

Public Class Form1
    Private vReloj As New Stopwatch()
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        vReloj.Reset()
        vReloj.Start()
        Dim vPrimos As Long() = getPrimes(9000000)
        vReloj.Stop()
        Debug.WriteLine("Se Calcularon los primeros " & vPrimos.Length & " en " & (vReloj.ElapsedMilliseconds / 1000) & " segundos.")
    End Sub
 
    Private Shared Function getPrimes(ByVal n As Long) As Long()
        If n < 3 Then
            If n = 2 Then
                Dim prime2 As Long() = {2}
                Return prime2
            Else
                Dim no_prime As Long() = {}
                Return no_prime
            End If
        End If
 
        Dim composite As New BitArray(n / 3)
        Dim d1 As Long = 8, d2 As Long = 8, p1 As Long = 3, p2 As Long = 7, s As Long = 7, s2 As Long = 3
        Dim i As Long = 0
        Dim len As Long = composite.Length
        Dim toggle As Boolean = False
 
        While s < len
 
            If Not composite(System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)) Then
                Dim inc As Long = p1 + p2
                Dim k As Long = s
 
                While k < len
                    composite(k) = True
                    k += inc
                End While
 
                k = s + s2
 
                While k < len
                    composite(k) = True
                    k += inc
                End While
            End If
 
            p1 += 2
            If InlineAssignHelper(toggle, Not toggle) Then
                s += d2
                d1 += 16
                p2 += 2
                s2 = p2
            Else
                s += d1
                d2 += 8
                p2 += 6
                s2 = p1
            End If
        End While
 
        Dim primes As New List(Of Long)()
        Dim log_n As Double = Math.Log(n)
 
        primes.Capacity = CInt((n / log_n) * (1 + 1.2762 / log_n))
        primes.Add(2)
        primes.Add(3)
 
        Dim p As Long = 5
        toggle = False
        i = 0
 
        While p <= n
            If Not composite(System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)) Then
                primes.Add(p)
            End If
            p += If((InlineAssignHelper(toggle, Not toggle)), 2, 4)
        End While
 
        Return primes.ToArray()
    End Function
 
    Private Shared Function InlineAssignHelper(Of T)(ByRef target As T, ByVal value As T) As T
        target = value
        Return value
    End Function
End Class
 

Public Class Form1
    Private vReloj As New Stopwatch()
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        vReloj.Reset()
        vReloj.Start()
        Dim vPrimos As List(Of Long) = getPrimes(99999999)
        vReloj.Stop()
        Debug.WriteLine("Se Calcularon los primeros " & vPrimos.Count & " en " & (vReloj.ElapsedMilliseconds / 1000) & " segundos.")
    End Sub
 
    Function getPrimes(ByVal vLimite As Long) As List(Of Long)
        Dim vNoEsPrimo(vLimite) As Boolean
        Dim vPrimos As New List(Of Long)
        For vPrimo As Long = 2 To vLimite
            If Not vNoEsPrimo(vPrimo) Then
                vPrimos.Add(vPrimo)
                For i As Long = vPrimo * 2 To vLimite Step vPrimo
                    vNoEsPrimo(i) = True
                Next
            End If
        Next
        Return vPrimos
    End Function
End Class