import java.util.*;
import java.util.stream.*;
import java.util.regex.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String s = "1) \\\\<@!1123> 2) \\\\\\<@!2123> 3) <@3123>test<@3456> 4) \\<@4123>test\\\\\\<@4456>";
		Pattern pattern = Pattern.compile("(?<!\\\\)(?:\\\\\\\\)*(<@!?\\d+>)");
		for (String t: pattern.matcher(s).results().flatMap(g -> Stream.of(g.group(1))).toArray(String[]::new)) {
			System.out.println(t); 
		} 
	}
}

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