9721
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
- 2
- Divisor Sum
- 9722
- Proper Divisor Sum (Aliquot Sum)
- 1
- 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
- 9720
- Möbius Function
- -1
- Radical
- 9721
- Omega Function (Ω)
- 1
- 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
- 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
- 166
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- yes
- Composite Number
- no
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- yes
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 1199
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Primes that remain prime through 3 iterations of function f(x) = 8x + 5.at n=13A023293
- Primes that remain prime through 4 iterations of function f(x) = 8x + 5.at n=1A023321
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 52 ones.at n=24A031820
- Arrange digits of cubes in descending order.at n=13A032554
- Primes p such that the decimal digits of p^2 can be partitioned into two or more nonzero squares.at n=26A048646
- Number of rooted trees with n nodes with every leaf at height 7.at n=18A048812
- Smallest value of x such that M(x) = -n, where M(x) is Mertens's function A002321.at n=32A051401
- Values of A (the short leg) of a Pythagorean triangle with A and C (the hypotenuse) both prime and part of a twin prime.at n=25A051642
- Primes p such that x^18 = 2 has no solution mod p, but x^6 = 2 has a solution mod p.at n=21A059664
- Primes p such that x^54 = 2 has no solution mod p, but x^6 = 2 has a solution mod p.at n=22A059665
- Primes p such that x^36 = 2 has no solution mod p, but x^12 = 2 has a solution mod p.at n=16A059668
- Primes p such that the greatest prime divisor of p-1 is 5.at n=33A061599
- a(1) = 1, a(n) = largest prime divisor of A057137(n).at n=6A073844
- a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.at n=6A075022
- Sum of the n-th row of A077339.at n=15A081929
- a(n) = 6*n^2 + 3*n + 1.at n=40A085473
- Primes p such that (p-11)/10 is also a prime.at n=41A089442
- Primes in which the unit place digit is 1 and the k-th most significant digit is prime (2,3,5,7) if k is prime else is composite (4,6,8,9,0).at n=25A089704
- Largest n-digit prime in which the unit place digit is 1 and the k-th most significant digit is prime (2,3,5,7) if k is prime else is composite (4,6,8,9,0).at n=2A089706
- When A032523 is a maximum; or, A091657 less duplicates.at n=15A091658