9999 has 12 divisors (see below), whose sum is σ = 15912.
Its totient is φ = 6000.
The previous prime is 9973. The next prime is 10007.
9999 is nontrivially palindromic in base 10.
It is a Cunningham number, because it is equal to 104-1.
It is a trimorphic number since its cube, 999700029999, ends in 9999.
It is not a de Polignac number, because 9999 - 25 = 9967 is a prime.
It is a nude number because it is divisible by every one of its digits.
9999 is a modest number, since divided by 999 gives 9 as remainder.
9999 is a lucky number.
9999 is a nontrivial repdigit in base 10.
It is a plaindrome in base 10.
It is a nialpdrome in base 10.
It is a zygodrome in base 10.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (9929) by changing a digit.
It is a Kaprekar number, because its square (99980001) can be partitioned into two parts whose sum is 9999.
It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 49 + ... + 149.
It is an arithmetic number, because the mean of its divisors is an integer number (1326).
29999 is an apocalyptic number.
9999 is a gapful number since it is divisible by the number (99) formed by its first and last digit.
9999 is a deficient number, since it is larger than the sum of its proper divisors (5913).
9999 is a wasteful number, since it uses less digits than its factorization.
9999 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 118 (or 115 counting only the distinct ones).
The product of its digits is 6561, while the sum is 36.
The square root of 9999 is about 99.9949998750.
The cubic root of 9999 is about 21.5436287315.
The spelling of 9999 in words is "nine thousand, nine hundred ninety-nine".