639971 has 4 divisors (see below), whose sum is σ = 641592. Its totient is φ = 638352.

The previous prime is 639959. The next prime is 639983. The reversal of 639971 is 179936.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (639959) and next prime (639983).

It is a cyclic number.

It is not a de Polignac number, because 639971 - 2⁶ = 639907 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639911) 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 3 ways as a sum of consecutive naturals, for example, 215 + ... + 1151.

It is an arithmetic number, because the mean of its divisors is an integer number (160398).

2⁶³⁹⁹⁷¹ is an apocalyptic number.

639971 is a deficient number, since it is larger than the sum of its proper divisors (1621).

639971 is an equidigital number, since it uses as much as digits as its factorization.

639971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1620.

The product of its digits is 10206, while the sum is 35.

The square root of 639971 is about 799.9818747947. The cubic root of 639971 is about 86.1760859440.

Subtracting from 639971 its sum of digits (35), we obtain a palindrome (639936).

The spelling of 639971 in words is "six hundred thirty-nine thousand, nine hundred seventy-one".