809840 has 40 divisors (see below), whose sum is σ = 1928448. Its totient is φ = 316160.

The previous prime is 809839. The next prime is 809843. The reversal of 809840 is 48908.

809840 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

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 809840.

It is not an unprimeable number, because it can be changed into a prime (809843) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4145 + ... + 4335.

2⁸⁰⁹⁸⁴⁰ is an apocalyptic number.

809840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 809840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (964224).

809840 is an abundant number, since it is smaller than the sum of its proper divisors (1118608).

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

809840 is a wasteful number, since it uses less digits than its factorization.

809840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 257 (or 251 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 809840 is about 899.9111067211. The cubic root of 809840 is about 93.2108370312.

The spelling of 809840 in words is "eight hundred nine thousand, eight hundred forty".