Option Explicit

Public Function RANDBETWEENAZ(Optional auto_generate As Boolean = True) As String
Static vector(0 To 26) As String
Dim s As String, i As Integer, p As Integer, q As Integer
'by VF
'Generates a pair of letters A-Z not repeated
'Vector is regenerated each time a couple of letters are extracted.
'If "auto_generate" is True or omitted, the Function doesn't regenerate the couple of letters.
'Otherwise every time the sheet is calcukated (or by pressing F9), a new string is recreate.

    Application.Volatile auto_generate
    If CInt(vector(0)) = 13 Then
        'reinitializing vector after two steps
        vector(0) = "0"
        For i = 1 To 26
            vector(i) = Chr(i + 64)
        Next
        
        'shuffling
        Randomize Timer
        For i = 1 To 1000
            p = Int(Rnd(1) * 26) + 1
            q = Int(Rnd(1) * 26) + 1
            s = vector(q)
            vector(q) = vector(p)
            vector(p) = s
        Next
    End If
    
    vector(25) = vector(1)
    vector(26) = vector(2)
    For i = 1 To 24
        vector(i) = vector(i + 2)
    Next
    s = vector(1) & vector(2)
    
    If s = "" Then s = RANDBETWEENAZ(auto_generate)
    vector(0) = CStr(CInt(vector(0)) + 1)
    RANDBETWEENAZ = s
    
End Function

'---------------------------------------------------------------------------------------
' Procedure : RandomAZ
' Author    : scossa
' Date      : 15/08/2015
' Purpose   : return a pair of different letters, each between A-Z
' arguments : if bVolatile is true or omitted, udf will be recalculated
'             at each sheet recalculation (or F9 pressing), and a new string is recreate
'---------------------------------------------------------------------------------------
'
Public Function RandomAZ(Optional ByVal bVolatile As Boolean = True) As String
  
  Dim sRet_ As String
  Dim cLetters As Collection
  Dim i As Byte
  
  Application.Volatile bVolatile
  
  Set cLetters = New Collection
  For i = 65 To 90
    cLetters.Add Chr(i)
  Next
  Randomize
  i = Int(Rnd(1) * 26) + 1
  sRet_ = cLetters(i)
  cLetters.Remove i
  Randomize
  i = Int(Rnd(1) * 25) + 1
  sRet_ = sRet_ & cLetters(i)
  
  RandomAZ = sRet_

End Function

'---------------------------------------------------------------------------------------
' Procedure : RandomAZ
' Author    : scossa
' Date      : 15/08/2015
' Purpose   : return a pair of different letters, each between A-Z
' arguments : if bVolatile is true or omitted, udf will be recalculated
'             at each sheet recalculation (or F9 pressing), and a new string is recreate
'---------------------------------------------------------------------------------------
'
Public Function RandomAZ(Optional ByVal bVolatile As Boolean = True) As String
  
  Dim sRet_ As String
  Dim cLetters As Collection
  Dim i As Byte
  
  Application.Volatile bVolatile
  
  Set cLetters = New Collection
  For i = 65 To 90
    cLetters.Add Chr(i)
  Next
  Randomize
  i = Int(Rnd(1) * 26) + 1
  sRet_ = cLetters(i)
  cLetters.Remove i
  Randomize
  i = Int(Rnd(1) * 25) + 1
  sRet_ = sRet_ & cLetters(i)
  
  RandomAZ = sRet_
  set cLetters = Nothing

End Function

=SE(IDENTICO(CODICE.CARATT(CASUALE.TRA(65;90));CODICE.CARATT(CASUALE.TRA(65;90)));CODICE.CARATT(CASUALE.TRA(66;90)-1) & CODICE.CARATT(CASUALE.TRA(65;89)+1);CODICE.CARATT(CASUALE.TRA(65;90))&CODICE.CARATT(CASUALE.TRA(65;90)))

Textomb
Io credo di averla trovata una soluzione, cercando di risolvere un altro quesito


Marius
Credo che la possibilità di lettere uguali non sia poca. E' la stessa soluzione che cercavo di ottimizzare nella altro quesito

=STRINGA.ESTRAI("ABACADAEAFAGAHAIAJAKALAMANAOAPAQARASATAUAVAWAXAYAZBABCBDBEBFBGBHBIBJBKBLBMBNBOBPBQBRBSBTBUBVBWBXBYBZCACBCDCECFCGCHCICJCK
CLCMCNCOCPCQCRCSCTCUCVCWCXCYCZDADBDCDEDFDGDHDIDJDKDLDMDNDODPDQDRDSDTDUDVDWDXDYDZEAEBECEDEFEGEHEIEJEKELEMENEOEPEQERESETEUEVEWEXEYEZFAFB"&
"FCFDFEFGFHFIFJFKFLFMFNFOFPFQFRFSFTFUFVFWFXFYFZGAGBGCGDGEGFGHGIGJGKGLGMGNGOGPGQGRGSGTGUGVGWGXGYGZHAHBHCHDHEHFHGHIHJHKHLHMHNHOHPHQ
HRHSHTHUHVHWHXHYHZIAIBICIDIEIFIGIHIJIKILIMINIOIPIQIRISITIUIVIWIXIYIZJAJBJCJDJEJFJGJHJIJKJLJMJNJOJPJQJRJSJTJUJVJWJXJYJZKAKBK"&
"CKDKEKFKGKHKIKJKLKMKNKOKPKQKRKSKTKUKVKWKXKYKZLALBLCLDLELFLGLHLILJLKLMLNLOLPLQLRLSLTLULVLWLXLYLZMAMBMCMDMEMFMGMHMIMJMKMLMNMOMPMQMR
MSMTMUMVMWMXMYMZNANBNCNDNENFNGNHNINJNKNLNMNONPNQNRNSNTNUNVNWNXNYNZOAOBOCODOEOFOGOHOIOJOKOLOMONOPOQOROSOTOUOVOWOXOYOZPAPBPC"&
"PDPEPFPGPHPIPJPKPLPMPNPOPQPRPSPTPUPVPWPXPYPZQAQBQCQDQEQFQGQHQIQJQKQLQMQNQOQPQRQSQTQUQVQWQXQYQZRARBRCRDRERFRGRHRIRJRKRLRMRNRORPRQ
RSRTRURVRWRXRYRZSASBSCSDSESFSGSHSISJSKSLSMSNSOSPSQSRSTSUSVSWSXSYSZTATBTCTDTETFTGTHTITJTKTLTMTNTOTPTQTRTSTUTVTWTXTYTZUAUBUCU"&
"DUEUFUGUHUIUJUKULUMUNUOUPUQURUSUTUVUWUXUYUZVAVBVCVDVEVFVGVHVIVJVKVLVMVNVOVPVQVRVSVTVUVWVXVYVZWAWBWCWD"&"WEWFWGWHWIWJWKWLWMWNW
OWPWQWRWSWTWUWVWXWYWZXAXBXCXDXEXFXGXHXIXJXKXLXMXNXOXPXQXRXSXTXUXVXWXYXZYAYBYCYDYEYFYGYHYIYJYKYLYMYNYOYPYQYRYSYTYUYVYWYXYZZAZBZ
CZDZEZFZGZHZIZJZKZLZMZNZOZPZQZRZSZTZUZVZWZXZY";DISPARI(CASUALE.TRA(1;1299));2)