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use strict;
use warnings;

my @nums = (17, 10, 20, 33, 30, 40, 10, 33, 40, 15, 16, 17);
my %values;

++$values{$_} for @nums;
print join "\n", map{"$_: $values{$_}"} sort {$a <=> $b} keys %values;
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which prints an ordered list of the unique values and their counts:

10: 2
15: 1
16: 1
17: 2
20: 1
30: 1
33: 2
40: 2
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