639649 has 4 divisors (see below), whose sum is σ = 649264. Its totient is φ = 630036.

The previous prime is 639647. The next prime is 639671. The reversal of 639649 is 946936.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 639649 - 2¹ = 639647 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639647) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4707 + ... + 4840.

It is an arithmetic number, because the mean of its divisors is an integer number (162316).

2⁶³⁹⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

639649 is a deficient number, since it is larger than the sum of its proper divisors (9615).

639649 is an equidigital number, since it uses as much as digits as its factorization.

639649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9614.

The product of its digits is 34992, while the sum is 37.

The square root of 639649 is about 799.7805949134. The cubic root of 639649 is about 86.1616304166.

The spelling of 639649 in words is "six hundred thirty-nine thousand, six hundred forty-nine".