16721
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 17
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 17472
- Proper Divisor Sum (Aliquot Sum)
- 751
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 15972
- Möbius Function
- 1
- Radical
- 16721
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 66
- 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
- Expansion of tan(log(1+x)/cos(x)).at n=7A009652
- Strong pseudoprimes to base 65.at n=13A020291
- Strong pseudoprimes to base 79.at n=17A020305
- Sums of 5 distinct powers of 4.at n=24A038473
- Number of bracketings of 0^0^0^...^0, with n 0's, giving the result 0, with conventions that 0^0 = 1^0 = 1^1 = 1, 0^1 = 0.at n=12A055113
- Concatenate n and the sum of factorials of the digits of n.at n=16A109016
- Row sums of triangle A131327.at n=18A131328
- a(1)=1, a(n)=a(n-1)+n if n even, a(n)=a(n-1)+n^2 if n is odd.at n=44A136047
- Semiprime terms in A136047.at n=12A136048
- A086892(11*n).at n=21A141460
- a(n) = A145818(2n-1).at n=39A145850
- Triangle of coefficients of polynomials defined by Binet form: P(n,x) = ((x + d)^n - (x - d)^n)/(2*d), where d = sqrt(x+4).at n=61A162517
- Constant term of the reduction by x^2 -> x+1 of the polynomial p(n,x) defined below in Comments.at n=17A192746
- Records in A214323.at n=10A214324
- Number of ordered ways of writing n as a sum of n tetrahedral numbers.at n=12A303170
- Odd composite integers m such that A087130(m) == 5 (mod m).at n=29A335671
- Odd composite integers m such that U(m)^2 == 1 (mod m) and V(m) == 5 (mod m), where U(m) and V(m) are the m-th generalized Lucas and Pell-Lucas numbers of parameters a=5 and b=-1, respectively.at n=17A337628
- Number of distinct sums i^3 + j^3 + k^3 for 1<=i<=j<=k<=n.at n=46A374713