9821
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 20
- Digital Root
- 2
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 11904
- Proper Divisor Sum (Aliquot Sum)
- 2083
- 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
- 7920
- Möbius Function
- -1
- Radical
- 9821
- 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
- 135
- 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
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Arrange digits of 2^n in descending order.at n=13A028910
- Numbers whose concatenation of prime factors (with multiplicity) is a square.at n=28A038693
- Denominators of continued fraction convergents to sqrt(566).at n=10A042085
- Odd numbers seen in decimal expansion of Pi (disregarding the decimal period) contiguous, smallest and distinct.at n=30A050817
- Numbers n such that n | 11^n + 10^n + 9^n + 8^n + 7^n + 6^n + 5^n.at n=28A057264
- a(n) is the first of a triple of consecutive integers, each of which is the product of three distinct primes.at n=19A066509
- Average of terms of n-th row of A077321.at n=34A077325
- Numbers n such that 2*10^n + 3 is prime.at n=18A081677
- Multiples of 23 whose digit reversal - 1 is also a multiple of 23.at n=15A166400
- Numbers n such that n!8 + 2 is prime.at n=46A204663
- Triangle read by rows: T(n,k) is the number of non-equivalent regular polygons with n+1 edges, one of which is rooted, which are dissected by non-intersecting diagonals into k regions, such that two such polygons are identified up to reflection along the rooted edge and twisting along the diagonals that does not affect the root edge (for 1 <= k <= n-1 and n >= 2).at n=76A232206
- Number of partitions of n into 6 parts such that every i-th smallest part (counted with multiplicity) is different from i.at n=38A244242
- Numbers n such that 11^n is the highest power of 11 dividing A240751(n).at n=44A286006
- Number of canonical forms for separation coordinates on hyperspheres S_n, ordered by increasing number of independent continuous parameters.at n=67A295380
- Positive integers k having no duplicated digit such that concatenating all successive absolute differences between two successive digits of k produces a divisor of k.at n=78A338641
- Odd composite integers m such that A004187(3*m-J(m,45)) == 7*J(m,45) (mod m) and gcd(m,45)=1, where J(m,45) is the Jacobi symbol.at n=40A340241
- Terms of A339863 that are congruent to 5 modulo 6: numbers k == 5 (mod 6) such that A005179(k-1) > A005179(k) < A005179(k+1) >A005179(k+2) < A005179(k+3).at n=44A349940
- Triangle read by rows: T(n, k) = Sum_{d=0..n-k} binomial(n, d)*StirlingS2(n-d, k)*8^(n-d-k), with 0 <= k <= n.at n=33A364071
- Square array A(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where column k is the expansion of B(x)^k, where B(x) is the g.f. of A384145.at n=51A384652