645640 has 16 divisors (see below), whose sum is σ = 1452780. Its totient is φ = 258240.

The previous prime is 645629. The next prime is 645641. The reversal of 645640 is 46546.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 636804 + 8836 = 798^2 + 94^2 .

It is not an unprimeable number, because it can be changed into a prime (645641) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8031 + ... + 8110.

2⁶⁴⁵⁶⁴⁰ is an apocalyptic number.

It is an amenable number.

645640 is an abundant number, since it is smaller than the sum of its proper divisors (807140).

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

645640 is a wasteful number, since it uses less digits than its factorization.

645640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16152 (or 16148 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 25.

The square root of 645640 is about 803.5172680161. The cubic root of 645640 is about 86.4297936801.

The spelling of 645640 in words is "six hundred forty-five thousand, six hundred forty".