643840 has 36 divisors (see below), whose sum is σ = 1545264. Its totient is φ = 257024.

The previous prime is 643781. The next prime is 643847. The reversal of 643840 is 48346.

It is not an unprimeable number, because it can be changed into a prime (643847) 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 3 ways as a sum of consecutive naturals, for example, 1029 + ... + 1531.

It is an arithmetic number, because the mean of its divisors is an integer number (42924).

2⁶⁴³⁸⁴⁰ 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 643840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (772632).

643840 is an abundant number, since it is smaller than the sum of its proper divisors (901424).

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

643840 is an equidigital number, since it uses as much as digits as its factorization.

643840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 524 (or 510 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 25.

The square root of 643840 is about 802.3964107597. The cubic root of 643840 is about 86.3493988114.

The spelling of 643840 in words is "six hundred forty-three thousand, eight hundred forty".