6555
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 16
- Divisor Sum
- 11520
- Proper Divisor Sum (Aliquot Sum)
- 4965
- 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
- 3168
- Möbius Function
- 1
- Radical
- 6555
- Omega Function (Ω)
- 4
- Little Omega Function (ω)
- 4
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- yes
- 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
- 49
- 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
- a(n) = (n-1)!! - (n-2)!!.at n=9A007911
- Ceiling of Gamma(n + 5/11)/Gamma(5/11).at n=8A020100
- Numbers having period-4 6-digitized sequences.at n=39A031197
- Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 25.at n=34A031523
- Number of series-reduced planted compound windmills with n leaves of 2 colors with no symmetries.at n=7A032174
- a(n) = (2*n-1)*(4*n-1).at n=29A033567
- Triangular numbers that have some nontrivial permutation of digits which is also triangular.at n=29A034291
- Number of partitions of n into parts not of the form 21k, 21k+10 or 21k-10. Also number of partitions with at most 9 parts of size 1 and differences between parts at distance 9 are greater than 1.at n=32A035988
- Number of multiples of 3 in 0..2^n-1 with an even sum of base-2 digits.at n=15A036557
- Numbers having three 8's in base 9.at n=27A043487
- Numbers having three 5's in base 10.at n=32A043511
- a(1)=6; if n = Product p_i^e_i, n>1, then a(n) = Product p_{i+1}^e_i * Product p_{i+2}^e_i.at n=33A045969
- Squarefree odd numbers with exactly 4 distinct prime factors.at n=37A046390
- 17-gonal (or heptadecagonal) numbers: a(n) = n*(15*n-13)/2.at n=30A051869
- Numbers k such that k divides the (right) concatenation of all numbers <= k written in base 12 (most significant digit on right).at n=12A061941
- Triangular numbers that contain exactly 2 different digits.at n=19A062691
- Composites for which the row of the prime-composite array (A063173) includes the leftmost element of both a zero-only antidiagonal and a zero-only diagonal(A067681).at n=39A063176
- Numbers k such that sigma(k^2 + 1) == 0 (mod k).at n=27A067719
- Triangular numbers with sum of digits = 21.at n=7A068131
- Triangular numbers in which neighboring digits differ at most by 1. Allowed neighbors of 9 are 0, 8 and 9.at n=16A068149