11991
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 18304
- Proper Divisor Sum (Aliquot Sum)
- 6313
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 6840
- Möbius Function
- -1
- Radical
- 11991
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
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
- yes
- Narcissistic Number
- no
- Collatz Steps
- 81
- 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
- Numbers whose square in base 2 is a palindrome.at n=4A003166
- Numbers k such that sigma(k) = sigma(k+6).at n=29A015866
- 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 72.at n=37A031570
- Triangle of numbers a(n,k), 0 <= k <= n: number of set partitions of {1,2,...,n} in which exactly k of the blocks have been distinguished.at n=40A049020
- a(n+1) = a(n)-th composite number, with a(1) = 11.at n=32A059407
- a(n) = p^2 + p + 1 where p runs through the primes.at n=28A060800
- Descending dungeons: a(10)=10; for n>10, a(n) = a(n-1) read as if it were written in base n.at n=11A121265
- Numbers of the form 110 + p^2. (where p is a prime).at n=28A138693
- a(n) = 2*binomial(n+4, 4) + n + 4.at n=17A177206
- Numbers n such that the greatest prime divisor p of n^2+1 has the property that (p - n)^2 + 1 = p.at n=37A206246
- The point to which the powers of n merge on an 8-digit calculator.at n=7A216070
- Numbers arising in computing the Turan function of cycles of length 4.at n=29A217004
- Odd numbers whose square's binary reversal is also a square.at n=3A229766
- Triangle read by rows: T(n,k) = Sum_{j=k..n} binomial(n,j)*Stirling_2(j,k)*Bell(n-j), where Bell(n) = A000110(n), for n >= 1, 0 <= k <= n-1.at n=32A244489
- G.f.: Sum_{n>=0} exp(-(1 + n^2*x)) * (1 + n^2*x)^n / n!.at n=4A245109
- Least integer k such that the n-th prime of form m^2+1 divides the composite number k^2+1.at n=19A255675
- Number of factorizations of m^n into 3 factors, where m is a product of exactly 3 distinct primes and each factor is a product of n primes (counted with multiplicity).at n=26A257464
- Length of period of Narayana sequence A000930 modulo n-th prime.at n=28A271901
- a(n) = A277715(n) / 3.at n=51A277716
- Numbers k with the property that the square root of the product of the digits of k is equal to the sum of the square roots of its digits.at n=23A281745