Question: How do I use Digits within a procedure?

I am trying to create a procedure like this: myproc := proc(x) Digits := x; sqrt(x) end proc; and then I want to plot the results like this: plot(myproc(x), x=2..20); However, I get an error: "Invalid assignment to Digits". The following works fine, however: seq(myproc(x), x=2..20); How can I solve this? Thanks.
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