16521
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 15
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 22032
- Proper Divisor Sum (Aliquot Sum)
- 5511
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 11012
- Möbius Function
- 1
- Radical
- 16521
- 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
- 66
- 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 n such that n divides the (right) concatenation of all numbers <= n written in base 22 (most significant digit on right).at n=31A061951
- Least k for which Omega(6k-1) + Omega(6k+1) >= n.at n=9A145194
- a(n+1)-+a(n)=prime, a(n+1)*a(n)=Average of twin prime pairs, a(1)=3,a(2)=10.at n=26A154496
- Number of binary strings of length n with no substrings equal to 0001 0100 or 1101.at n=17A164467
- Number of 0..n arrays x(0..7) of 8 elements with zero 5th differences.at n=21A200275
- Triangle of coefficients of polynomials v(n,x) jointly generated with A209162; see the Formula section.at n=52A209163
- Years >= 1801 in which Christmas falls in Sukkot.at n=17A222419
- Number of (n+1) X (3+1) 0..2 arrays with no element unequal to a strict majority of its horizontal, diagonal and antidiagonal neighbors, with values 0..2 introduced in row major order.at n=7A231391
- If x^2 + 2*y^2 is prime for all positive integers x and y with m = x*y then m is in the sequence.at n=9A287799
- Number of n X n 0..1 arrays with every element equal to 1, 2, 4, 5 or 7 king-move adjacent elements, with upper left element zero.at n=5A298576
- Number of nX6 0..1 arrays with every element equal to 1, 2, 4, 5 or 7 king-move adjacent elements, with upper left element zero.at n=5A298580
- T(n,k)=Number of nXk 0..1 arrays with every element equal to 1, 2, 4, 5 or 7 king-move adjacent elements, with upper left element zero.at n=60A298582
- a(n) = Sum_{k=3..n} binomial(k-1,2) * floor(n/k).at n=44A366970
- Expansion of e.g.f. exp(x*cosh(x) + x^2*sinh(x)/2).at n=8A389688