640644 has 24 divisors (see below), whose sum is σ = 1507968. Its totient is φ = 211680.

The previous prime is 640631. The next prime is 640649. The reversal of 640644 is 446046.

It is not an unprimeable number, because it can be changed into a prime (640649) by changing a digit.

640644 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, 2229 + ... + 2499.

It is an arithmetic number, because the mean of its divisors is an integer number (62832).

2⁶⁴⁰⁶⁴⁴ is an apocalyptic number.

It is an amenable number.

640644 is an abundant number, since it is smaller than the sum of its proper divisors (867324).

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

640644 is a wasteful number, since it uses less digits than its factorization.

640644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 475 (or 473 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 24.

The square root of 640644 is about 800.4023987970. The cubic root of 640644 is about 86.2062832435.

The spelling of 640644 in words is "six hundred forty thousand, six hundred forty-four".