99840 has 80 divisors (see below), whose sum is σ = 343728. Its totient is φ = 24576.

The previous prime is 99839. The next prime is 99859. The reversal of 99840 is 4899.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a nialpdrome in base 10.

It is a zygodrome in base 2.

It is a junction number, because it is equal to n+sod(n) for n = 99798 and 99807.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 99840.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7674 + ... + 7686.

2⁹⁹⁸⁴⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 99840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (171864).

99840 is an abundant number, since it is smaller than the sum of its proper divisors (243888).

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

99840 is a wasteful number, since it uses less digits than its factorization.

99840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39 (or 23 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 99840 is about 315.9746825301. The cubic root of 99840 is about 46.3911199812.

It can be divided in two parts, 99 and 840, that added together give a palindrome (939).

The spelling of 99840 in words is "ninety-nine thousand, eight hundred forty".