639678 has 32 divisors (see below), whose sum is σ = 1411200. Its totient is φ = 192096.

The previous prime is 639677. The next prime is 639679. The reversal of 639678 is 876936.

It is an interprime number because it is at equal distance from previous prime (639677) and next prime (639679).

It is a Harshad number since it is a multiple of its sum of digits (39).

Its product of digits (54432) is a multiple of the sum of its prime divisors (216).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639671) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 4533 + ... + 4671.

It is an arithmetic number, because the mean of its divisors is an integer number (44100).

2⁶³⁹⁶⁷⁸ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639678, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (705600).

639678 is an abundant number, since it is smaller than the sum of its proper divisors (771522).

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

639678 is a wasteful number, since it uses less digits than its factorization.

639678 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216.

The product of its digits is 54432, while the sum is 39.

The square root of 639678 is about 799.7987246802. The cubic root of 639678 is about 86.1629325107.

The spelling of 639678 in words is "six hundred thirty-nine thousand, six hundred seventy-eight".