1. Introducing a different topic; in point of fact
   - by the bye, incidentally, apropos

Encyclopedia: By the way

• 1st-class mail
• 2
• 2 Chronicles
• 2 Esdras
• 2 Kings
• 2 Maccabees
• 2 Samuel
• 2-dimensional
• 2-hitter
• 2-hydroxybenzoic acid
• 2-methylpropenoic acid
• 20
• 20-20 vision
• 20/20
• 200
• 200th
• 20th
• 21
• 21st
• 22
• 22-carat gold
• 22-karat gold
• 22nd
• 23
• 23rd