640728064 has 44 divisors (see below), whose sum is σ = 1308180384. Its totient is φ = 313524224.

The previous prime is 640728047. The next prime is 640728071. The reversal of 640728064 is 460827046.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 41472 + ... + 54784.

Almost surely, 2^640728064 is an apocalyptic number.

640728064 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640728064, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (654090192).

640728064 is an abundant number, since it is smaller than the sum of its proper divisors (667452320).

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

640728064 is a wasteful number, since it uses less digits than its factorization.

640728064 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13380 (or 13362 counting only the distinct ones).

The product of its (nonzero) digits is 64512, while the sum is 37.

The square root of 640728064 is about 25312.6068195277. The cubic root of 640728064 is about 862.1005368281.

The spelling of 640728064 in words is "six hundred forty million, seven hundred twenty-eight thousand, sixty-four".