99978 has 16 divisors (see below), whose sum is σ = 210720. Its totient is φ = 31536.

The previous prime is 99971. The next prime is 99989. The reversal of 99978 is 87999.

It is a happy number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (99971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 325 + ... + 552.

It is an arithmetic number, because the mean of its divisors is an integer number (13170).

2⁹⁹⁹⁷⁸ is an apocalyptic number.

99978 is an abundant number, since it is smaller than the sum of its proper divisors (110742).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (105360).

99978 is a wasteful number, since it uses less digits than its factorization.

99978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 901.

The product of its digits is 40824, while the sum is 42.

The square root of 99978 is about 316.1929790492. The cubic root of 99978 is about 46.4124842547.

The spelling of 99978 in words is "ninety-nine thousand, nine hundred seventy-eight".