Number 21
The number 21 is the 9th Fibonacci number, the 6th triangular number. It has 4 divisors and a digital root of 3. Explore its full properties below, or find words and phrases with a gematria value of 21.
21
Divisors: 4
1, 3, 7, 21
Sum: 32
Prev Triangular: 15
6th Triangular Number
Next Triangular: 28
Prev Fibonacci: 13
9th Fibonacci Number
Next Fibonacci: 34
Mathematical Properties
Golden Number17,711
Reduced Digit Sum3
Magic Constant4,641
Digital Root3
Octal17(25)
Duodecimal25(19)
Hexadecimal33(15)
Binary10101
21st Values
Prime73
Triangular231
Square441
Star2,521
Pentagonal651
Cube9,261
Tetrahedral1,771
Square Pyramidal3,311
Fibonacci10,946
Harshad45
Happy Number176