Private Sub CommandButton1_Click()
Dim prem$, n As Variant, i As Integer
prem = Left(Sheets(1).Name, 1)
n = Mid(Sheets(1).Name, 2, 30)
If IsNumeric(n) Then
'On Error Resume Next 'en cas de feuille de même nom...
For i = 1 To Sheets.Count
Sheets(i).Name = prem & Format(n + i - 1, Application.Rept("0", Len(n)))
Next
End If
End Sub