2821
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 13
- Digital Root
- 4
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 3584
- Proper Divisor Sum (Aliquot Sum)
- 763
- 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
- 2160
- Möbius Function
- -1
- Radical
- 2821
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- no
- 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
- 35
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- 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
- yes
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Number of points of norm <= n^2 in square lattice.at n=30A000328
- Octagonal numbers: n*(3*n-2). Also called star numbers.at n=31A000567
- Deceptive nonprimes: composite numbers k that divide the repunit R_{k-1}.at n=6A000864
- Number of sublattices of index n in generic 3-dimensional lattice.at n=29A001001
- Fermat pseudoprimes to base 2, also called Sarrus numbers or Poulet numbers.at n=10A001567
- Carmichael numbers: composite numbers k such that a^(k-1) == 1 (mod k) for every a coprime to k.at n=4A002997
- Pseudoprimes to base 3.at n=13A005935
- Pseudoprimes to base 5.at n=8A005936
- Pseudoprimes to base 6.at n=12A005937
- Pseudoprimes to base 10.at n=14A005939
- 4-dimensional analog of centered polygonal numbers: a(n) = n(n+1)*(n^2+n+4)/12.at n=13A006007
- Number of one-sided hexagonal polyominoes with n cells.at n=7A006535
- Coordination sequence T1 for Zeolite Code AFT.at n=40A008026
- Coordination sequence T2 for Zeolite Code AFX.at n=40A009865
- Orders of cyclotomic polynomials containing a coefficient the absolute value of which is >= 3.at n=39A013591
- Odd octagonal numbers: (2n+1)*(6n+1).at n=15A014641
- Powers of sqrt(24) rounded down.at n=5A017976
- Powers of fourth root of 24 rounded down.at n=10A018114
- Fermat pseudoprimes to base 4.at n=22A020136
- Pseudoprimes to base 8.at n=37A020137