16581
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 22112
- Proper Divisor Sum (Aliquot Sum)
- 5531
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 11052
- Möbius Function
- 1
- Radical
- 16581
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 2
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
- 40
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- 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
- Numbers k such that tau(k) = tau(k+1) mod 691, where tau is Ramanujan's tau function A000594.at n=25A121733
- Least k such that A046694(k) = A046694(k+1) = ... = 0 are n consecutive zeros starting with A046694(k), where A046694 = Ramanujan tau numbers mod 691.at n=1A134670
- Numbers k such that k^6 - 2 and k^6 + 2 are both primes.at n=26A154938
- Last term where no prime sums occur in A161190 in a 4-diagonal set of 24 terms.at n=7A161193
- Half the number of (n+1) X 3 binary arrays with no 2 X 2 subblock containing exactly one 1.at n=4A184190
- Half the number of (n+1)X6 binary arrays with no 2X2 subblock containing exactly one 1.at n=1A184193
- T(n,k)=Half the number of (n+1)X(k+1) binary arrays with no 2X2 subblock containing exactly one 1.at n=16A184197
- T(n,k)=Half the number of (n+1)X(k+1) binary arrays with no 2X2 subblock containing exactly one 1.at n=19A184197
- a(n) = floor((n + 1/2)^3).at n=25A219085
- a(n) = floor(M(g(n-1)+1, ..., g(n))), where M = harmonic mean and g(n) = n^3.at n=25A227012
- Numbers k for which the sum of digits of sigma(k) = the product of digits of sigma(k).at n=18A277217
- a(n) is the least integer k such that k*prime(n) is in A346113, or 0 if no such k exists.at n=25A346177
- a(n) is the side length of the simple perfect squared square of order n leading to a maximum of the ratio of the side length of its smallest element A349205(n) to its total side length.at n=16A349206
- Number of vertices formed in a square by straight line segments when connecting the four corner vertices to the points dividing the sides into n equal parts.at n=31A355949
- Numbers whose square is of the form k + reversal of digits of k, for some k.at n=47A356648
- E.g.f. A(x) satisfies A(x) = exp(x * A(x))/(1 - x*A(x)^3).at n=4A377889