9987
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 33
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 13320
- Proper Divisor Sum (Aliquot Sum)
- 3333
- 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
- 6656
- Möbius Function
- 1
- Radical
- 9987
- 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
- 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=16A031597
- G.f.: Sum_{k >= 1} x^k/(1-x^k)^(k+1).at n=55A081543
- Numbers k such that k, k+2, k+4, k+6, k+8 are semiprimes.at n=31A092127
- Numbers k such that k, k+2, k+4, k+6, k+8, k+10 are semiprimes.at n=10A092128
- Minimal peaks in digital expansions of Pi: positions of peaks equal to 1.at n=10A105275
- Composite numbers between largest n-digit prime and the smallest (n+1) digit prime.at n=30A109936
- a(n) = A160799(n)/4.at n=33A160807
- Numbers with rounded up arithmetic mean of digits = 9.at n=42A178369
- Values x for records of minima of the positive distance d between an 11th power of a positive integer x and a square of an integer y such that d = x^13 - y^2 (x<>k^2 and y<>k^13).at n=51A179799
- Number of distinct solutions of sum{i=1..3}(x(2i-1)*x(2i)) = 1 (mod n), with x() in 0..n-1.at n=12A180805
- Composite numbers and 1 which yield a prime whenever a 7 is inserted anywhere in them, including at the beginning or end.at n=34A216168
- Magic constants of the magic cubes 3 X 3 X 3 composed of prime numbers.at n=14A239671
- Consider a number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that sigma(n)-n = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(j)*10^(j-1)})} + Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(k-j+1)*10^(i-j)})} (see example below).at n=6A240902
- a(n) is the largest n-digit number whose truncation after its first k digits is divisible by the k-th Fibonacci number for k = 1..n.at n=3A242809
- Magic sums of 3 X 3 semimagic squares composed of positive triangular numbers.at n=38A269060
- Where records occur in A283832.at n=22A285191
- a(n) is the smallest number that can be expressed as the sum of the smallest number of powers with different exponents greater than one in n different ways (for unitary bases, the smallest possible exponents are considered).at n=54A383122