16821
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 18
- Digital Root
- 9
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 4
Divisibility
- Divisor Count
- 16
- Divisor Sum
- 28800
- Proper Divisor Sum (Aliquot Sum)
- 11979
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 9504
- Möbius Function
- 0
- Radical
- 1869
- Omega Function (Ω)
- 5
- 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
- 97
- 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
- Number of partitions satisfying cn(1,5) <= cn(0,5) + cn(2,5) and cn(1,5) <= cn(0,5) + cn(3,5) and cn(4,5) <= cn(0,5) + cn(2,5) and cn(4,5) <= cn(0,5) + cn(3,5).at n=42A039874
- Numbers whose base-7 representation contains exactly four 0's.at n=13A043396
- a(n) = a(1) + a(2) + ... + a(n-1) - a(m) for n >= 3, where m = 2*n - 2 - 2^(p+1) and p is the unique integer such that 2^p < n-1 <= 2^(p+1), starting with a(1) = 1 and a(2) = 3.at n=17A049919
- Triangle T(n,k) giving number of 4 X k polyominoes with n cells (n >= 4, 1<=k<=n-3).at n=52A059684
- Integers that are Rhonda numbers to more than one base.at n=33A100988
- a(n) = n^2*(n+1)*(4*n^3 - 2*n^2 + n + 3)/12.at n=6A101380
- Triangle read by rows: coefficient of x^n in the Taylor expansion of x/(1 - m*x - x^4) in row n, column m=1..n+2.at n=34A117742
- G.f. satisfies: A(x) = x + A(x^2/(1-x)^2).at n=13A119685
- Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, 0, 0), (0, -1, 1), (0, 0, 1), (0, 1, -1), (1, -1, 0)}.at n=10A148316
- a(n) = 841*n + 1.at n=19A158404
- a(n) = 20*n^2 + 1.at n=29A158493
- Numbers k such that phi(phi(k)) = sigma(rad(k)).at n=25A173748
- Potential magic constants of 9 X 9 magic squares composed of consecutive primes.at n=30A191679
- a(0) = 12, after which, if a(n-1) = product_{k >= 1} (p_k)^(c_k), then a(n) = (1/2) * (1 + product_{k >= 1} (p_{k+1})^(c_k)), where p_k indicates the k-th prime, A000040(k).at n=36A246342
- Group the natural numbers such that the first group is (1) then (2),(3),(4,5),(6,7,8),... with the n-th group containing F(n) sequential terms where F(n) is the n-th Fibonacci number (A000045(n)). Sequence gives the sum of terms in the n-th group.at n=11A301809
- Number of compositions of n into parts with distinct multiplicities and with exactly nine parts.at n=17A321779
- Number of partitions of n into colored blocks of equal parts, such that all colors from a set of size ten are used and the colors are introduced in increasing order.at n=18A327293