645920 has 48 divisors (see below), whose sum is σ = 1669248. Its totient is φ = 234240.

The previous prime is 645907. The next prime is 645937. The reversal of 645920 is 29546.

It is a self number, because there is not a number n which added to its sum of digits gives 645920.

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 645920.

It is an unprimeable number.

645920 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1577 + ... + 1943.

It is an arithmetic number, because the mean of its divisors is an integer number (34776).

2⁶⁴⁵⁹²⁰ 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 645920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (834624).

645920 is an abundant number, since it is smaller than the sum of its proper divisors (1023328).

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

645920 is a wasteful number, since it uses less digits than its factorization.

645920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 393 (or 385 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 645920 is about 803.6914830953. The cubic root of 645920 is about 86.4422861138.

The spelling of 645920 in words is "six hundred forty-five thousand, nine hundred twenty".