7921
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 3
- Divisor Sum
- 8011
- Proper Divisor Sum (Aliquot Sum)
- 90
- 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
- 7832
- Möbius Function
- 0
- Radical
- 89
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 1
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- no
- Perfect Square
- yes
- 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
- 52
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- Squarefree Number
- no
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- yes
- Achilles Number
- no
- Perfect Power
- yes
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Squares of primes.at n=23A001248
- a(n) = a(n-1) + a(n-3) + a(n-4), a(0) = a(1) = a(2) = 1, a(3) = 2.at n=20A006498
- Squared Fibonacci numbers: a(n) = F(n)^2 where F = A000045.at n=11A007598
- sec(sin(arctanh(x)))=1+1/2!*x^2+9/4!*x^4+201/6!*x^6+7921/8!*x^8...at n=4A012061
- sec(tan(arcsinh(x)))=1+1/2!*x^2+9/4!*x^4+201/6!*x^6+7921/8!*x^8...at n=4A012168
- a(n) = (F(n+1)+L(n)+n)^2 where F(n) are the Fibonacci numbers (A000045) and L(n) are the Lucas numbers (A000032).at n=8A014718
- Squares of odd Fibonacci numbers.at n=7A014728
- a(n) is the sum over all floor(k^3/n), k=0 to n inclusive.at n=30A014818
- Numbers n such that tau(sigma(n))= tau(tau(n)).at n=27A015730
- Odd squares: a(n) = (2n+1)^2. Also centered octagonal numbers.at n=44A016754
- a(n) = (3n+2)^2.at n=30A016790
- a(n) = (4*n + 1)^2.at n=22A016814
- a(n) = (5*n + 4)^2.at n=17A016898
- a(n) = (6*n + 5)^2.at n=14A016970
- a(n) = (7*n + 5)^2.at n=12A017042
- a(n) = (8*n + 1)^2.at n=11A017078
- a(n) = (9*n + 8)^2.at n=9A017258
- a(n) = (10*n + 9)^2.at n=8A017378
- a(n) = (11*n+1)^2.at n=8A017402
- a(n) = (12*n + 5)^2.at n=7A017582