4021
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 7
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 4022
- Proper Divisor Sum (Aliquot Sum)
- 1
- 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
- 4020
- Möbius Function
- -1
- Radical
- 4021
- Omega Function (Ω)
- 1
- Little Omega Function (ω)
- 1
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
- no
- Narcissistic Number
- no
- Collatz Steps
- 69
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- yes
- Composite Number
- no
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- yes
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 556
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Artiads: the primes p == 1 (mod 5) for which Fibonacci((p-1)/5) is divisible by p.at n=20A001583
- Where the prime race among 7k+1, ..., 7k+6 changes leader.at n=31A007354
- Number of subsequences of [ 1,...,n ] in which each even number has an odd neighbor.at n=13A007481
- a(n) = 3*a(n-1) + 2*a(n-2), with a(0)=2, a(1)=7.at n=6A007484
- Coordination sequence for MgZn2, Mg position.at n=16A009939
- Numbers k such that the continued fraction for sqrt(k) has period 27.at n=14A020366
- Primes that remain prime through 2 iterations of function f(x) = 5x + 2.at n=45A023252
- Primes that remain prime through 3 iterations of function f(x) = 5x + 2.at n=9A023283
- Primes of form x^2+65*y^2.at n=27A033241
- Positive numbers having the same set of digits in base 5 and base 10.at n=27A037433
- Coordination sequence T1 for Zeolite Code STT.at n=42A038428
- a(n)=(s(n)+6)/10, where s(n)=n-th base 10 palindrome that starts with 4.at n=24A043083
- Primes with first digit 4.at n=25A045710
- Primes for which golden mean is a cubic residue.at n=41A047652
- Size of range 1..m generatable from the digits of an n-digit integer and + - x /.at n=5A048175
- a(n) = a(n-1) + a(m) for n >= 4, where m = 2^(p+1) + 2 - n and p is the unique integer such that 2^p < n - 1 <= 2^(p+1), starting with a(1) = a(2) = 1 and a(3) = 2.at n=43A050029
- First member of a prime triple in a p^2 + p - 1 progression.at n=24A057324
- Primes p such that x^67 = 2 has no solution mod p.at n=6A059330
- Primes whose sum of digits is 7.at n=25A062337
- Numbers where k-th digit from right is either 0 or k.at n=11A063013