645664 has 12 divisors (see below), whose sum is σ = 1271214. Its totient is φ = 322816.

The previous prime is 645661. The next prime is 645683. The reversal of 645664 is 466546.

It can be written as a sum of positive squares in only one way, i.e., 501264 + 144400 = 708^2 + 380^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10057 + ... + 10120.

2⁶⁴⁵⁶⁶⁴ is an apocalyptic number.

It is an amenable number.

645664 is a deficient number, since it is larger than the sum of its proper divisors (625550).

645664 is a wasteful number, since it uses less digits than its factorization.

645664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20187 (or 20179 counting only the distinct ones).

The product of its digits is 17280, while the sum is 31.

The square root of 645664 is about 803.5322022172. The cubic root of 645664 is about 86.4308646017.

The spelling of 645664 in words is "six hundred forty-five thousand, six hundred sixty-four".