Retired Uniform Numbers in the American League
Retired Uniform Numbers in the National League
NBA players with two different numbers retired
Last player to wear No. 42 for each MLB team
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Bill Russell's No. 6 Joins Rare Class of Retired Jersey Numbers - The New York Times
MLB allows more players to wear No. 21 to honor Roberto Clemente – NBC Sports Chicago
Should Tom Brady's #12 jersey number be retired league-wide? Considering a rare honor for the Patriots legend
Retired number - Wikipedia
Has the NFL Ever Retired a Player's Jersey Number League-Wide?
History of retired numbers dates back to Lou Gehrig Day
Yankees retired numbers: A look at all of the jersey numbers players cannot wear in the Bronx
Lakers Retire Kobe Bryant's Jersey Numbers
History of retired numbers dates back to Lou Gehrig Day