Prime Number

Function to create prime number
Syntax =PRIME(Starting Number, Ending Number)

Private Function PRIME(St, En As Long)
Dim Ans As String
For x = St To En
    For y = 2 To x - 1
        If x Mod y = 0 Then GoTo 20:
    Next y
    Ans = Ans & x & ","
20:
Next x
PRIME = Ans
End Function

Link: ExcelForum

Update to verify a Prime:
=AND(MOD(A2;ROW(INDIRECT("2:"&INT(SQRT(A2))))))
Link: Chandoo.org