Function BESSK(N, X)
    If N < 2 Then
        Print "bad argument N in BESSK"
        Exit Function
    End If
    TOX = 2# / X
    BKM = BESSK0(X)
    BK = BESSK1(X)
    For J = 1 To N - 1
        BKP = BKM + J * TOX * BK
        BKM = BK
        BK = BKP
    Next J
    BESSK = BK
End Function