8421
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 15
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 12864
- Proper Divisor Sum (Aliquot Sum)
- 4443
- 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
- 4800
- Möbius Function
- -1
- Radical
- 8421
- 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
- no
- Narcissistic Number
- no
- Collatz Steps
- 127
- Smith Number
- yes
- 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
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Number of walks on cubic lattice starting and finishing on the xy plane and never going below it.at n=6A005572
- Pseudoprimes to base 20.at n=30A020148
- Pseudoprimes to base 22.at n=41A020150
- Pseudoprimes to base 29.at n=43A020157
- Strong pseudoprimes to base 83.at n=10A020309
- Triangle of Gaussian binomial coefficients [ n,k ] for q = 20.at n=13A022184
- Triangle of Gaussian binomial coefficients [ n,k ] for q = 20.at n=11A022184
- Number of terms in n-th derivative of a function composed with itself 4 times.at n=13A022812
- a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-1)*a(1) for n >= 3, with initial terms 2,1.at n=7A025228
- a(n) = Sum_{i=0..floor(n/2)} T(2i,n-2i), array T as in A049723.at n=24A049726
- Triangle of numbers arising in enumeration of walks on cubic lattice.at n=21A052179
- Expansion of (1-x)(1+x)/(1 - x - x^2 - x^3 + x^5).at n=17A052977
- a(n) = n^3 + n^2 + n + 1.at n=20A053698
- Sum of distinct powers of 20; i.e., numbers with digits in {0,1} base 20; i.e., write n in base 2 and read as if written in base 20.at n=15A063012
- a(n) = (20^n - 1)/19.at n=4A064108
- Successive left concatenation of floor(k/2) beginning with n until we reach 1.at n=7A068657
- Interprimes (A024675) which are of the form s*prime, s=21.at n=22A075296
- Numbers k such that 2^k - prime(k) is prime.at n=14A078583
- Let P(k) = floor(k/2). Start with n, apply P repeatedly until reach 1. a(n) = concatenation of numbers obtained.at n=14A083177
- a(n) is the largest number such that all of a(n)'s length-n substrings are distinct and divisible by 21.at n=1A093221