Get my function UniqRandInt() from www.sulprobil.com,
select 20 cells and enter

=UniqRandInt(1000)

with CTRL+SHIFT+ENTER (array formula) to get 20 different
numbers or

=INDEX($A$1:$A$1000,UniqRandInt(1000))

as an array formula to get 20 different random names if
these are in cells A1:A1000, for example.

HTH,
Bernd