[euler/prob003] add more 6ish version that works with current Rakudo

Author: gerdr

euler/prob003-gerdr.pl

@@ -0,0 +1,15 @@
+use v6;
+
+sub largest-prime-factor($n is copy) {
+	my @primes;
+	for 2, 3, *+2 ... * -> $p {
+		next if $p %% any @primes.grep({ $_ * $_ <= $p or last});
+		@primes.push($p);
+		while $n %% $p {
+			$n div= $p;
+			return $p if $p >= $n;
+		}
+	}
+}
+
+say largest-prime-factor(600851475143);