640660 has 24 divisors (see below), whose sum is σ = 1362816. Its totient is φ = 252960.

The previous prime is 640649. The next prime is 640663. The reversal of 640660 is 66046.

640660 = T₅₆ + T₅₇ + ... + T₁₅₈.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640663) 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, 1905 + ... + 2215.

It is an arithmetic number, because the mean of its divisors is an integer number (56784).

2⁶⁴⁰⁶⁶⁰ is an apocalyptic number.

It is an amenable number.

640660 is an abundant number, since it is smaller than the sum of its proper divisors (722156).

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

640660 is a wasteful number, since it uses less digits than its factorization.

640660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 423 (or 421 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 22.

The square root of 640660 is about 800.4123937071. The cubic root of 640660 is about 86.2070009010.

The spelling of 640660 in words is "six hundred forty thousand, six hundred sixty".