Properties of the Number 21

Twenty-One

Basics

Value: 20 → 21 → 22

Parity: odd

Prime: No

Previous Prime: 19

Next Prime: 23

Digit Sum: 3

Digital Root: 3

Palindrome: No

Factorization: 3 × 7

Divisors: 1, 3, 7, 21

Polygonal

Triangular: Yes

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

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Representations

Binary: 10101

Octal: 25

Duodecimal: 19

Hexadecimal: 15

Square: 441

Square Root: 4.58257569495584

Classification

Fibonacci: Yes

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

No sequences found.