About

Ii9 (nine) is the natural number the proceeds 8 and precedes 10. In words, it is "Nine".

Properties

• 9 is the third square number.
• In base-10, a number is divisible by 9 if the sum of the digits is divisible by 9. For example: 126 -> 1+2+6 = 9; 136 -> 1+3+6 = 10. 126 is a multiple of 9, and 136 is not.
• 9 is the sum of the first 3 factorial numbers.
• 9 is the third semiprime.

Times Tables

1 x 9 = 9

2 x 9 = 18

3 x 9 = 27

4 x 9 = 36

5 x 9 = 45

6 x 9 = 54

7 x 9 = 63

8 x 9 = 72

9 x 9 = 81

10 x 9 = 90

11 x 9 = 99

12 x 9 = 108

Significance

• Bananas develop on the "banana hearts" of banana trees, which each have nine hands.
• There are nine stickers on each face of a Rubik's Cube.
• Baseball per regulation half (9 per team).
• Sudoku is 9x9.
• Tic-tac-toe has 9 squares on the grid.
• 9 is the highest UK GCSE exam grade.
• Kitsunes have nine tails.
• There are nine planets in the old Solar System model.
• There are nine stage positions.

Bases

9's value is:

• 1001 in Binary.
• 100 in Ternary.
• 21 in Quaternary.
• 14 in Quinary.
• 13 in Heximal.
• 12 in Septimal.
• 11 in Octal.
• 10 in Nonary.