640686 has 8 divisors (see below), whose sum is σ = 1281384. Its totient is φ = 213560.

The previous prime is 640669. The next prime is 640687. The reversal of 640686 is 686046.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

640686 is an admirable number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640687) by changing a digit.

640686 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 53385 + ... + 53396.

It is an arithmetic number, because the mean of its divisors is an integer number (160173).

2⁶⁴⁰⁶⁸⁶ is an apocalyptic number.

640686 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

640686 is a wasteful number, since it uses less digits than its factorization.

640686 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 106786.

The product of its (nonzero) digits is 6912, while the sum is 30.

The square root of 640686 is about 800.4286351699. The cubic root of 640686 is about 86.2081670691.

It can be divided in two parts, 640 and 686, that added together give a triangular number (1326 = T₅₁).

The spelling of 640686 in words is "six hundred forty thousand, six hundred eighty-six".