9991
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 28
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 4
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 10192
- Proper Divisor Sum (Aliquot Sum)
- 201
- 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
- 9792
- Möbius Function
- 1
- Radical
- 9991
- 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
- no
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 166
- 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
- a(n) = (8*n+1)*(8*n+7).at n=12A001533
- 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 99.at n=17A031597
- Number of partitions of n with equal number of parts congruent to each of 2, 3 and 4 (mod 5).at n=54A035581
- a(n) is the smallest composite number c such that A002110(n) + c is prime.at n=23A038771
- Numbers having three 9's in base 10.at n=28A043527
- a(n) = Sum_{d|n, n/d=3 mod 4} d^3.at n=62A050466
- a(n) is the largest number which can be formed with no zeros, using least number of digits and having digit sum = n.at n=27A061219
- Centered 15-gonal numbers: a(n) = (15*n^2 - 15*n + 2)/2.at n=36A069128
- Numbers k for which the sums of prime factors (ignoring multiplicity) of sigma(k) and phi(k) are equal but the sets of prime factors of sigma and phi are different.at n=38A081378
- a(n) is the smallest k such that number of non-unitary prime divisors of central binomial coefficient, A000984(k) = C(2*k,k) equals n.at n=21A081393
- a(n) is the smallest value of k such that number of non-unitary prime divisors of k-th Catalan number, A000108(k) = C(2*k,k)/(k+1) equals n.at n=21A081395
- a(n) = (6*n+1)*(6*n+7).at n=16A085026
- a(n) = prime(n)*prime(n+2).at n=24A090076
- Smallest m such that A098371(m) = n.at n=34A098373
- Near-repdigit semiprimes with 9 as repeated digit.at n=24A105990
- Composite numbers between largest n-digit prime and the smallest (n+1) digit prime.at n=34A109936
- Product of the n-th sexy prime pair.at n=15A111192
- Products of two primes that are not Chen primes.at n=27A115719
- Number of blocks of size >1 in all partitions of an n-set.at n=8A124325
- Number of partitions of n into parts that are odd or == +- 4 mod 10.at n=44A134157