Twin primes: Difference between revisions
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There are 3424506 twin primes <= 10^9
</pre>
=={{header|Visual Basic}}==
{{works with|Visual Basic|4}}
{{works with|Visual Basic|5}}
{{works with|Visual Basic|6}}
<lang vb>Function IsPrime(x As Long) As Boolean
Dim i As Long
If x Mod 2 = 0 Then
Exit Function
Else
For i = 3 To Int(Sqr(x)) Step 2
If x Mod i = 0 Then Exit Function
Next i
End If
IsPrime = True
End Function
Function TwinPrimePairs(max As Long) As Long
Dim p1 As Boolean, p2 As Boolean, count As Long, i As Long
p2 = True
For i = 5 To max Step 2
p1 = p2
p2 = IsPrime(i)
If p1 And p2 Then count = count + 1
Next i
TwinPrimePairs = count
End Function
Sub Test(x As Long)
Debug.Print "Twin prime pairs below" + Str(x) + ":" + Str(TwinPrimePairs(x))
End Sub
Sub Main()
Test 10
Test 100
Test 1000
Test 10000
Test 100000
Test 1000000
Test 10000000
End Sub</lang>
{{out}}
<pre>Twin prime pairs below 10: 2
Twin prime pairs below 100: 8
Twin prime pairs below 1000: 35
Twin prime pairs below 10000: 205
Twin prime pairs below 100000: 1224
Twin prime pairs below 1000000: 8169
Twin prime pairs below 10000000: 58980</pre>
=={{header|Wren}}==
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