Function ISPRIME ( N as long) As Boolean

Select Case N
   Case 0
        ISPRIME =false    
        Exit Function
   Case 1
        ISPRIME =false
        Exit Function
   Case 2
        ISPRIME =true
        Exit Function
 End Select
   
         
If N mod 2 = 0 Then
     ISPRIME = false
     Exit Function
End If
    
Dim M as long
M = Int(Sqr(N)) +1
For i=3 To M Step 2
  If N mod i = 0 Then
     ISPRIME = false
     Exit Function
  End if
Next  i
    
ISPRIME = true
    
End Function