640402660 has 24 divisors (see below), whose sum is σ = 1381194360. Its totient is φ = 249237504.

The previous prime is 640402613. The next prime is 640402663. The reversal of 640402660 is 66204046.

It can be written as a sum of positive squares in 4 ways, for example, as 375429376 + 264973284 = 19376^2 + 16278^2 .

It is not an unprimeable number, because it can be changed into a prime (640402663) 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, 431965 + ... + 433444.

It is an arithmetic number, because the mean of its divisors is an integer number (57549765).

Almost surely, 2^640402660 is an apocalyptic number.

It is an amenable number.

640402660 is an abundant number, since it is smaller than the sum of its proper divisors (740791700).

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

640402660 is a wasteful number, since it uses less digits than its factorization.

640402660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 865455 (or 865453 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 28.

The square root of 640402660 is about 25306.1782970088. The cubic root of 640402660 is about 861.9545682636.

The spelling of 640402660 in words is "six hundred forty million, four hundred two thousand, six hundred sixty".