Subtracting from 9998 its reverse (8999), we obtain a palindrome (999).
9998 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a semiprime because it is the product of two primes.
It is a Curzon number.
It is a nialpdrome in base 10.
It is a congruent number.
It is an unprimeable number.
9998 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
9998 is a wasteful number, since it uses less digits than its factorization.
9998 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 5001.
The square root of 9998 is about 99.9899994999. The cubic root of 9998 is about 21.5429105148.
The spelling of 9998 in words is "nine thousand, nine hundred ninety-eight".