21

domain: N

Properties

Digital Properties

Digit Count
2
Digit Sum
3
Digital Root
3
Palindromic Number
no
Repdigit
no
Automorphic
no
Kaprekar Number
no
Multiplicative Persistence
1

Divisibility

Divisor Count
4
Divisor Sum
32
Proper Divisor Sum (Aliquot Sum)
11
Abundant Number
no
Perfect Number
no
Deficient Number
yes
Highly Composite
no
Weird Number
no
Untouchable Number
no
Primitive Abundant
no

Derived Values

Euler's Totient
12
Möbius Function
1
Radical
21
Omega Function (Ω)
2
Little Omega Function (ω)
2

Special

Factorial
no
Catalan Number
no
Bell Number
no
Motzkin Number
yes
Primorial
no

Figurate Numbers

Fibonacci Number
yes
Triangular Number
yes
Perfect Square
no
Perfect Cube
no
Pentagonal Number
no
Hexagonal Number
no
Lucas Number
no
Tetrahedral Number
no
Pell Number
no
Tribonacci Number
no
Pronic Number
no

Recreational

Happy Number
no
Harshad Number
yes
Narcissistic Number
no
Collatz Steps
7
Smith Number
no

Classification

Natural
yes
Even
no
Odd
yes

Primality

Prime
no
Composite Number
yes
Semiprime
yes
Squarefree Number
yes
Prime Power
no
Prime Factorization
no
Twin Prime
no
Mersenne Prime
no
Sophie Germain Prime
no
Safe Prime
no
Powerful Number
no
Achilles Number
no
Perfect Power
no
Smooth Number
no
Carmichael Number
no

Names

German
einundzwanzig· ordinal: einundzwanzigste
English
twenty-one· ordinal: twenty-first
Spanish
veintiuno· ordinal: 21º
French
vingt et un· ordinal: vingt et unième
Italian
ventuno· ordinal: 21º
Latin
viginti unus· ordinal: 21.
Portuguese
vinte e um· ordinal: 21º

Appears in sequences