640784 has 20 divisors (see below), whose sum is σ = 1285260. Its totient is φ = 309120.

The previous prime is 640777. The next prime is 640793. The reversal of 640784 is 487046.

It can be written as a sum of positive squares in 2 ways, for example, as 313600 + 327184 = 560^2 + 572^2 .

It is a Harshad number since it is a multiple of its sum of digits (29).

It is an unprimeable number.

640784 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 3 ways as a sum of consecutive naturals, for example, 227 + ... + 1154.

It is an arithmetic number, because the mean of its divisors is an integer number (64263).

2⁶⁴⁰⁷⁸⁴ is an apocalyptic number.

It is an amenable number.

640784 is an abundant number, since it is smaller than the sum of its proper divisors (644476).

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

640784 is a wasteful number, since it uses less digits than its factorization.

640784 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1418 (or 1412 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 29.

The square root of 640784 is about 800.4898500293. The cubic root of 640784 is about 86.2125623421.

The spelling of 640784 in words is "six hundred forty thousand, seven hundred eighty-four".