640720 has 20 divisors (see below), whose sum is σ = 1489860. Its totient is φ = 256256.

The previous prime is 640691. The next prime is 640727. The reversal of 640720 is 27046.

It can be written as a sum of positive squares in 2 ways, for example, as 322624 + 318096 = 568^2 + 564^2 .

It is a tau number, because it is divible by the number of its divisors (20).

640720 is a modest number, since divided by 720 gives 640 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3925 + ... + 4084.

It is an arithmetic number, because the mean of its divisors is an integer number (74493).

2⁶⁴⁰⁷²⁰ is an apocalyptic number.

It is an amenable number.

640720 is an abundant number, since it is smaller than the sum of its proper divisors (849140).

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

640720 is a wasteful number, since it uses less digits than its factorization.

640720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8022 (or 8016 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 19.

The square root of 640720 is about 800.4498735086. The cubic root of 640720 is about 86.2096920105.

Adding to 640720 its reverse (27046), we get a palindrome (667766).

The spelling of 640720 in words is "six hundred forty thousand, seven hundred twenty".