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Karim El Ahmadi, a retired Moroccan-Dutch professional footballer, commonly wore the jersey number 21 throughout his career. This number held significance for El Ahmadi, as he wore it for several prominent clubs, including Feyenoord, Aston Villa, and Al-Ittihad. The number 21 became synonymous with El Ahmadi's playing style, characterized by his versatility, defensive prowess, and ability to contribute offensively.