If you have office 365, then I think you could use the textjoin and sequence functions (I don't have sequence, but I think this would be how it would look if A1=14):
=textjoin(".",,sequence(A1))
Otherwise, I know this will work if you at least have textjoin (office 2016):
=textjoin(".",,row(indirect("1:"&A1)))
And, if you don't have textjoin, then I'm not sure you can do it with native excel functions and would have to resort to a vba user defined function.
