9840 has 40 divisors (see below), whose sum is σ = 31248. Its totient is φ = 2560.

The previous prime is 9839. The next prime is 9851. The reversal of 9840 is 489.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Smith number, since the sum of its digits (21) coincides with the sum of the digits of its prime factors.

It is a nialpdrome in base 3 and base 10.

It is a congruent number.

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, 220 + ... + 260.

2⁹⁸⁴⁰ 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 9840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (15624).

9840 is an abundant number, since it is smaller than the sum of its proper divisors (21408).

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

9840 is a wasteful number, since it uses less digits than its factorization.

9840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57 (or 51 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 9840 is about 99.1967741411. The cubic root of 9840 is about 21.4288253938.

The spelling of 9840 in words is "nine thousand, eight hundred forty".