Sort function in excel

i have a question about sor function in excel:

i need to sort the column A:3 to A:100 from smallest to largest, but in this column A, i want that column A:20 would not be sorted and just leave it as it is.is it possible to do this?

You'd need a macro to do it, but this should work...

Sub SortWithException()

Const sSORT_RANGE = "A1:A100"
Const sEXCEPTION = "A20"

Dim lExceptionValue As Long
Dim rngMatchException As Range

lExceptionValue = Range(sEXCEPTION).Value

Range(sSORT_RANGE).Sort Range(sSORT_RANGE), xlAscending

Set rngMatchException = Range(sSORT_RANGE).Find(lExceptionValue, lookat:=xlWhole)

If rngMatchException Is Nothing Then
  'Oh dear
Else
  rngMatchException.Delete shift:=xlShiftUp
  Range(sEXCEPTION).Insert shift:=xlShiftDown
  Range(sEXCEPTION).Value = lExceptionValue
End If

End Sub