640764 has 48 divisors (see below), whose sum is σ = 1764000. Its totient is φ = 200448.

The previous prime is 640741. The next prime is 640771. The reversal of 640764 is 467046.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

640764 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 15 ways as a sum of consecutive naturals, for example, 1662 + ... + 2010.

It is an arithmetic number, because the mean of its divisors is an integer number (36750).

2⁶⁴⁰⁷⁶⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640764, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (882000).

640764 is an abundant number, since it is smaller than the sum of its proper divisors (1123236).

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

640764 is a wasteful number, since it uses less digits than its factorization.

640764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 379 (or 371 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 27.

The square root of 640764 is about 800.4773575811. The cubic root of 640764 is about 86.2116653840.

640764 divided by its sum of digits (27) gives a palindrome (23732).

The spelling of 640764 in words is "six hundred forty thousand, seven hundred sixty-four".