MAIN_LOOP is a label. They can be used on flow control structures, bare blocks and any other statements. They can be used with next, last and goto.

".." is the range operator.

for my $var (LIST) is a foreach loop.

Together, they are optimized into a counting loop, basically a more readable version of

for (my $number_to_check=3; $number_to_check<=200; ++$number_to_check)
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