To subscript a hash, say $aminoacids{ $the_key }. (In your case, the keys are numeric so you may as well be using an array?)

This interpolates in a string, too, so you can say:

print "$aminoacids{$i} $aminoacids{$j} $aminoacids{$k}\n";

Though you can use the more idiomatic hash slice and select several things at once.

print join " ", @aminoacids{$i, $j, $k}; # note the '@'
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