639967 has 4 divisors (see below), whose sum is σ = 646056. Its totient is φ = 633880.

The previous prime is 639959. The next prime is 639983. The reversal of 639967 is 769936.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 639967 - 2³ = 639959 is a prime.

It is a super-2 number, since 2×639967² = 819115522178, which contains 22 as substring.

It is a Duffinian number.

639967 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2884 + ... + 3097.

It is an arithmetic number, because the mean of its divisors is an integer number (161514).

2⁶³⁹⁹⁶⁷ is an apocalyptic number.

639967 is a deficient number, since it is larger than the sum of its proper divisors (6089).

639967 is a wasteful number, since it uses less digits than its factorization.

639967 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6088.

The product of its digits is 61236, while the sum is 40.

The square root of 639967 is about 799.9793747341. The cubic root of 639967 is about 86.1759064020.

The spelling of 639967 in words is "six hundred thirty-nine thousand, nine hundred sixty-seven".