6721
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 16
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 8064
- Proper Divisor Sum (Aliquot Sum)
- 1343
- 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
- 5520
- Möbius Function
- -1
- Radical
- 6721
- Omega Function (Ω)
- 3
- 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
- 44
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- 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
- Bruckman-Lucas pseudoprimes: k | (L_k - 1), where k is composite and L_k = Lucas numbers A000032.at n=6A005845
- Numbers k for which 10k+1, 10k+3, 10k+7 and 10k+9 are primes.at n=27A007811
- Pseudoprimes to base 48.at n=38A020176
- Pseudoprimes to base 93.at n=45A020221
- Pseudoprimes to base 95.at n=28A020223
- Strong pseudoprimes to base 48.at n=12A020274
- Numbers k such that the continued fraction for sqrt(k) has period 70.at n=19A020409
- Number of block permutations on an n-set.at n=5A023997
- a(n) = A024733(n+3)/7.at n=11A024734
- a(n) = (d(n) - r(n))/5, where d = A026037 and r is the periodic sequence with fundamental period (1,2,0,2,0).at n=44A026039
- Cycle of 2 steps possible for 'concatenate a(n) and nextprime(a(n)) is a prime'.at n=41A034592
- Composite n coprime to 5 such that Fibonacci(n) == Legendre(n,5) (mod n).at n=4A049062
- Row sums of triangle A035469.at n=4A049119
- a(n) = (n+1)*(n+2)*(n+3)*(9n+4)/24.at n=10A051798
- Triangle: self-converse semigroups of order n with k idempotents.at n=22A058118
- Number of self-converse semigroups of order n with 2 idempotents.at n=5A058120
- Triangle of Stirling numbers of order 5.at n=14A059024
- Dimension of the space of weight n cuspidal newforms for Gamma_1( 79 ).at n=26A063352
- Composite numbers m such that phi(m)*sigma(m) is divisible by m-1.at n=18A065149
- Triangle of Gandhi polynomial coefficients.at n=15A065755