Seven is the fourth prime number.

Also:

• A heptagon has 7 sides
• A tetrahemihexahedron, a pentagonal prism, and a pentagrammic prism have 7 faces
• 7 is a lucky number
• 7 is a heptagonal number
• 7 is a Mersenne prime
• 7 is a double Mersenne prime
• 7 is a palindromic number.