Note that variable l (lower case L) is a really bad variable to use. BAD IDEA, since there is very little to distinguish between l and the number 1. In the font used as I am typing, the two are almost indistinguishable. (For some reason, they change the font when the text of an answer is displayed. Why does that seem silly to me?)
Surely you can select n-L random INTEGERS, all of which lie between 2 and n-1. Do so without replacement, so randperm is appropriate.
help randperm
Then just delete the comparable elements from the string vector.
