Простой RegEx (\d+)\* должен сделать трюк.
(\d+)\*
var line = "14*x1 + 2*x2 + 3*x3 = 2"; var matches = Regex.Matches(line, @"(\d+)\*"); // [] { 14, 2 , 3 } var numbers = matches.Select(x => double.Parse(x.Groups[1].Value)).ToArray();