7581
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 12
- Divisor Sum
- 12192
- Proper Divisor Sum (Aliquot Sum)
- 4611
- 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
- 4104
- Möbius Function
- 0
- Radical
- 399
- Omega Function (Ω)
- 4
- 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
- yes
- Harshad Number
- yes
- Narcissistic Number
- no
- Collatz Steps
- 176
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- Squarefree Number
- no
- 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
- Dedekind numbers or Dedekind's problem: number of monotone Boolean functions of n variables, number of antichains of subsets of an n-set, number of elements in a free distributive lattice on n generators, number of Sperner families.at n=5A000372
- a(n) = Sum_{k=0..n} C(n-k,3k).at n=17A003522
- Number of antichains (or order ideals) in the poset B_4 X [n]; or size of the distributive lattice J(B_4 X [n]).at n=2A006363
- Numbers k that divide s(k), where s(1)=1, s(j)=7*s(j-1)+j.at n=38A014854
- a(n) = a(n-3) + a(n-4), with a(0)=1, a(1)=a(2)=0, a(3)=1.at n=51A017817
- Sequence satisfies T^2(a)=a, where T is defined below.at n=51A027588
- Sorted k-factorial numbers (numbers of form k-1 excluded).at n=23A028687
- Sorted factorial and k-factorial numbers (numbers of form k-1 excluded).at n=29A028688
- Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 58.at n=20A031556
- Numbers n such that n | 12^n + 11^n + 10^n + 9^n.at n=44A057239
- Numbers primitive with respect to having more than one factorization into S-primes. See related sequences for definition.at n=41A057950
- Generalized sum of divisors function: third diagonal of A060044.at n=35A060045
- Integers n > 879 such that the 'Reverse and Add!' trajectory of n joins the trajectory of 879.at n=38A063052
- a(n) = 21*n^2.at n=19A064762
- Numbers that are sums of divisors of the odd squares; Intersection of A065764 and A065766, written in ascending order and duplicates removed.at n=39A065768
- Numbers n such that n*phi(n-1) is a perfect square.at n=15A069069
- Numbers n such that sum of digits of n equals the squarefree part of n.at n=45A070274
- Expansion of 1/(1-3*x-2*x^2-2*x^3).at n=7A077831
- Number of positions that are exactly n moves from the starting position in the Rashkey Type 1 puzzle.at n=13A079844
- Numbers n for which 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=16A096846