using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var str = "Теоретики3 и 2п4423рактики палинд4442рома выделили\n" +
				  "2многочис2ленные4 погран24ичные2 с пал24инд4ром4м формы";
 
		foreach (Match match in Regex.Matches(str, @"(?=\w*(?!\d)\w)(?=\w*\d)\w+", RegexOptions.IgnoreCase))
			Console.WriteLine(match.Value);
	}
}

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