recursive alphabet for order number

Private Sub generateORNumber()
        Dim con As New SqlConnection(ConnectString())
        Dim cd As New SqlCommand
        Dim lrd As SqlDataReader
        Try
            con.Open()
            cd.Connection = con
            cd.CommandText = "SELECT count(ornumber) as co,AlphabetID FROM BlueRoomTransactions group by AlphabetID"
            lrd = cd.ExecuteReader()
            While lrd.Read()
                ornum = Convert.ToString(lrd("co"))
                alpID = Convert.ToString(lrd("AlphabetID"))
            End While
        Catch ex As Exception
        Finally
            con.Close()
        End Try
        ornum = ornum + 1
        totalORNUM2 = ornum - 1

        txtORNumber.Text = "OR" & Date.Today.ToString("MMddyy") & alphRecursive().ToString & ornum.ToString.PadLeft(4, "0")


    End Sub


    Private Function alphRecursive() As String
        Dim alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray()

        If ornum > 1 Then
            alpID += 1
            c = alpID
            ''Reset ornum to zero(0) and add another alphabet on the existing string like 'AA,AB' after it reaches the designated ornum like 1
            If c >= alphabet.Length Then
                ornum = ornum - totalORNUM2
                c = 0
                Return alphRecursive(c \ alphabet.Length) & alphabet(c Mod alphabet.Length)
            Else
                ornum = ornum - totalORNUM2
                Return "" & alphabet(c Mod alphabet.Length)
            End If
        Else

            Return "" & alphabet(c Mod alphabet.Length)

        End If


    End Function