643820 has 12 divisors (see below), whose sum is σ = 1352064. Its totient is φ = 257520.

The previous prime is 643781. The next prime is 643847. The reversal of 643820 is 28346.

It is a happy number.

It is a hoax number, since the sum of its digits (23) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16076 + ... + 16115.

It is an arithmetic number, because the mean of its divisors is an integer number (112672).

2⁶⁴³⁸²⁰ is an apocalyptic number.

It is an amenable number.

643820 is an abundant number, since it is smaller than the sum of its proper divisors (708244).

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

643820 is a wasteful number, since it uses less digits than its factorization.

643820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32200 (or 32198 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 643820 is about 802.3839479950. The cubic root of 643820 is about 86.3485046939.

The spelling of 643820 in words is "six hundred forty-three thousand, eight hundred twenty".