639978 has 8 divisors (see below), whose sum is σ = 1279968. Its totient is φ = 213324.

The previous prime is 639959. The next prime is 639983. The reversal of 639978 is 879936.

It is a happy number.

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

639978 is an admirable number.

It is a nialpdrome in base 15.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 639978.

It is an unprimeable 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, 53326 + ... + 53337.

It is an arithmetic number, because the mean of its divisors is an integer number (159996).

2⁶³⁹⁹⁷⁸ is an apocalyptic number.

639978 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.

639978 is a wasteful number, since it uses less digits than its factorization.

639978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 106668.

The product of its digits is 81648, while the sum is 42.

The square root of 639978 is about 799.9862498818. The cubic root of 639978 is about 86.1764001407.

Subtracting from 639978 its sum of digits (42), we obtain a palindrome (639936).

The spelling of 639978 in words is "six hundred thirty-nine thousand, nine hundred seventy-eight".