using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var strs = new List<string> { "[45645]","[5456]","[PB15] [DEC]","[PB16] []"};
    	foreach (var str in strs) {
    		var result = Regex.Matches(str, @"\[[^][]+]")
    			.Cast<Match>()
    			.Select(x => x.Value)
    			.Where(m => m.Any(Char.IsDigit))
    			.ToList();
    		foreach (var s in result)
        		Console.WriteLine(s);
    	}
	}
}

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