645904 has 40 divisors (see below), whose sum is σ = 1468160. Its totient is φ = 269568.

The previous prime is 645901. The next prime is 645907. The reversal of 645904 is 409546.

It is an interprime number because it is at equal distance from previous prime (645901) and next prime (645907).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (645901) 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, 8137 + ... + 8215.

It is an arithmetic number, because the mean of its divisors is an integer number (36704).

2⁶⁴⁵⁹⁰⁴ 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 645904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (734080).

645904 is an abundant number, since it is smaller than the sum of its proper divisors (822256).

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

645904 is a wasteful number, since it uses less digits than its factorization.

645904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 167 (or 161 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 645904 is about 803.6815289653. The cubic root of 645904 is about 86.4415723577.

The spelling of 645904 in words is "six hundred forty-five thousand, nine hundred four".