Here I'm.
So, the correct sintax is
cell.InitializeFormula(1,1,"HYPERLINK(""http://www.google.it"",""Google"")")
No "=" prefix.
Complete url with "http//"
No formulas in italian language ....
I think you told me before, I dont' know where I was losting doing test
but the "2+3" was the right starting point
Then in Excel the link works fine and the cell content become
="http://www.google.it" COLLEG.IPERTESTUALE("Google")
Thank you very much for your support.