week 150 task 2

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diff --git a/challenge-150/cheok-yin-fung/perl/ch-2.pl b/challenge-150/cheok-yin-fung/perl/ch-2.pl
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+# The Weekly Challenge 150
+# Task 2 Square-Free Numbers
+# Usage: $ ch-2.pl [upper_bound]
+
+use v5.22.0;
+use warnings;
+
+my $N = $ARGV[0] || 500;
+
+say join ", ", sq_free($N)->@*;
+
+
+
+sub sq_free {
+    my $n = $_[0];
+    my @is_sqfree = (1) x ($n+1);
+
+    my $sqrtn = int sqrt $n;
+    for my $i (2..$sqrtn) {
+        for my $j (1..$n/$i) {
+           $is_sqfree[$i*$i*$j] = 0;
+        }
+    }
+    return [grep {$is_sqfree[$_]} (1..$n)];
+}
+
+
+
+use Test::More tests => 1;
+use Test::Deep;
+cmp_deeply(sq_free(30), [1, 2, 3, 5, 6, 7, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 26, 29, 30]);
+
+# REF: https://stackoverflow.com/a/5313337 ,
+#      http://mathworld.wolfram.com/Squarefree.html