2
domain: N
Properties
Digital Properties
- Digit Count
- 1
- Digit Sum
- 2
- Digital Root
- 2
- Palindromic Number
- yes
- Repdigit
- yes
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 0
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 3
- Proper Divisor Sum (Aliquot Sum)
- 1
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Highly Composite
- yes
- Weird Number
- no
- Untouchable Number
- yes
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 1
- Möbius Function
- -1
- Radical
- 2
- Omega Function (Ω)
- 1
- Little Omega Function (ω)
- 1
Special
- Factorial
- yes
- Catalan Number
- yes
- Bell Number
- yes
- Motzkin Number
- yes
- Primorial
- yes
Figurate Numbers
- Fibonacci Number
- yes
- Triangular Number
- no
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- no
- Lucas Number
- yes
- Tetrahedral Number
- no
- Pell Number
- yes
- Tribonacci Number
- yes
- Pronic Number
- yes
Recreational
- Happy Number
- no
- Harshad Number
- yes
- Narcissistic Number
- yes
- Collatz Steps
- 1
- Smith Number
- no
Classification
- Natural
- yes
- Even
- yes
- Odd
- no
Primality
- Prime
- yes
- Composite Number
- no
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- yes
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 1
- Perfect Power
- no
- Smooth Number
- yes
- Carmichael Number
- no
Names
- German
- zwei· ordinal: zweite
- English
- two· ordinal: second
- Spanish
- dos· ordinal: segundo
- French
- deux· ordinal: deuxième
- Italian
- due· ordinal: secondo
- Latin
- duo· ordinal: secundus
- Portuguese
- dois· ordinal: segundo
Appears in sequences
- Number of groups of order n.at n=4A000001
- Number of groups of order n.at n=6A000001
- Number of groups of order n.at n=9A000001
- Number of groups of order n.at n=10A000001
- Number of groups of order n.at n=14A000001
- Number of groups of order n.at n=21A000001
- Number of groups of order n.at n=22A000001
- Number of groups of order n.at n=25A000001
- Number of groups of order n.at n=26A000001
- Number of groups of order n.at n=34A000001
- Number of groups of order n.at n=38A000001
- Number of groups of order n.at n=39A000001
- Number of groups of order n.at n=45A000001
- Number of groups of order n.at n=46A000001
- Number of groups of order n.at n=49A000001
- Number of groups of order n.at n=55A000001
- Number of groups of order n.at n=57A000001
- Number of groups of order n.at n=58A000001
- Number of groups of order n.at n=62A000001
- Number of groups of order n.at n=74A000001