6821
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 17
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 4
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 7200
- Proper Divisor Sum (Aliquot Sum)
- 379
- 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
- 6444
- Möbius Function
- 1
- Radical
- 6821
- 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
- 137
- 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 that are the sum of 9 positive 7th powers.at n=29A003376
- Numbers that are the sum of 6 nonzero 8th powers.at n=8A003384
- Numbers that are the sum of at most 6 nonzero 8th powers.at n=38A004879
- a(n) = ceiling(n*phi^15), where phi is the golden ratio, A001622.at n=5A004970
- Number of column-convex polyominoes with perimeter n.at n=6A006026
- Cycle class sequence c(n) (the number of true cycles of length n in which a certain node is included) for zeolite VNI = VPI-9 Rb44K4[Zn24Si96O240].48H2O starting with a T1 atom.at n=12A019252
- a(n) = [ a(n-1)/a(1) ] + [ a(n-3)/a(3) ] + [ a(n-5)/a(5) ] + ..., for n >= 3.at n=29A022866
- (d(n)-r(n))/5, where d = A008778 and r is the periodic sequence with fundamental period (0,3,1,0,1).at n=55A026053
- a(n) = A026998(2*n, n+4).at n=3A027003
- a(n) = T(n, 2*n-6), T given by A027960.at n=11A027968
- a(0)=1, a(1)=1, a(n) = 3*a(n-1) + a(n-2) + 1.at n=8A033538
- Denominators of continued fraction convergents to sqrt(357).at n=7A041677
- Numerators of continued fraction convergents to sqrt(979).at n=5A042894
- Numbers whose base-4 representation contains exactly three 1's and four 2's.at n=14A045104
- Nearest integer to log(n^n)^(1 + log(1 + log(n))).at n=16A062450
- Nearest integer to log(n)^sqrt(n).at n=43A062464
- A Chebyshev S-sequence with Diophantine property.at n=3A078368
- a(1)=4, then least semiprime > a(n-1) such that when all in the sequence are concatenated together they form a prime.at n=24A085703
- Numbers n such that the sum of the first n primes is divisible by n + 1.at n=10A098074
- Denominator of next-best approximation to harmonic numbers. a(n) = Denominator of (A055573(n)-1)th convergent of n-th harmonic number, Sum_{k=1..n} 1/k.at n=11A113124