7821
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 18
- Digital Root
- 9
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 12
- Divisor Sum
- 12480
- Proper Divisor Sum (Aliquot Sum)
- 4659
- 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
- 4680
- Möbius Function
- 0
- Radical
- 2607
- 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
- no
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 101
- 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
- a(n) is nonsquarefree and is sum of first k nonsquarefrees for some k.at n=33A013935
- Pseudoprimes to base 80.at n=43A020208
- Numbers k such that the continued fraction for sqrt(k) has period 56.at n=37A020395
- Numerators of continued fraction convergents to sqrt(93).at n=8A041166
- Engel expansion of 1/log(2) = 1.4427...at n=12A059183
- Sum of the remainders when n^2 is divided by squares less than n.at n=38A067459
- Row sums of triangle A084408.at n=25A084411
- a(1) = 1 then the least multiple of odd numbers not odd multiples of 5, (3,7,9,11,13,17,19,21,23,27,29,...) such that every partial concatenation is noncomposite.at n=39A110433
- Numbers k such that k + sigma(k) is a triangular number.at n=35A115904
- a(n)= 4*a(n-1) +13*a(n-2) -44*a(n-3) -57*a(n-4) +120*a(n-5) +63*a(n-6) -56*a(n-7) +6*a(n-8).at n=4A121798
- Numbers n such that n^3 is zeroless pandigital.at n=32A124628
- Number of planar triangular n X n X n nonnegative integer grids with mirror symmetry about one altitude with every similarly oriented 5 X 5 X 5 subtriangle summing to 11.at n=16A154084
- a(n) = 729*n - 198.at n=10A156772
- A transform of the Motzkin numbers.at n=30A157143
- Fibonacci-x^x where x is largest integer such that x^x is smaller than Fibonacci.at n=18A174255
- Potential magic constants of 9 X 9 magic squares composed of consecutive primes.at n=8A191679
- Number of (n+1)X(n+1) -4..4 symmetric matrices with every 2X2 subblock having sum zero and one, two or three distinct values.at n=6A211494
- Number of n X 2 arrays of the minimum value of corresponding elements and their horizontal, vertical, diagonal or antidiagonal neighbors in a random, but sorted with lexicographically nondecreasing rows and columns, 0..2 n X 2 array.at n=22A219211
- Number of nondecreasing -5..5 vectors of length n whose dot product with some nondecreasing -5..5 vector equals n.at n=5A226408
- T(n,k)=Number of nondecreasing -k..k vectors of length n whose dot product with some nondecreasing -k..k vector equals n.at n=50A226410