645840 has 160 divisors (see below), whose sum is σ = 2499840. Its totient is φ = 152064.

The previous prime is 645839. The next prime is 645851. The reversal of 645840 is 48546.

645840 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28069 + ... + 28091.

It is an arithmetic number, because the mean of its divisors is an integer number (15624).

2⁶⁴⁵⁸⁴⁰ is an apocalyptic number.

645840 is a gapful number since it is divisible by the number (60) 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 645840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1249920).

645840 is an abundant number, since it is smaller than the sum of its proper divisors (1854000).

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

645840 is a wasteful number, since it uses less digits than its factorization.

645840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58 (or 46 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 27.

The square root of 645840 is about 803.6417112122. The cubic root of 645840 is about 86.4387172155.

It can be divided in two parts, 645 and 840, that added together give a triangular number (1485 = T₅₄).

The spelling of 645840 in words is "six hundred forty-five thousand, eight hundred forty".