639665 has 12 divisors (see below), whose sum is σ = 832284. Its totient is φ = 471744.

The previous prime is 639647. The next prime is 639671. The reversal of 639665 is 566936.

It can be written as a sum of positive squares in 6 ways, for example, as 97969 + 541696 = 313^2 + 736^2 .

It is not a de Polignac number, because 639665 - 2⁶ = 639601 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 467 + ... + 1223.

It is an arithmetic number, because the mean of its divisors is an integer number (69357).

2⁶³⁹⁶⁶⁵ is an apocalyptic number.

639665 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

639665 is a deficient number, since it is larger than the sum of its proper divisors (192619).

639665 is a wasteful number, since it uses less digits than its factorization.

639665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 788 (or 775 counting only the distinct ones).

The product of its digits is 29160, while the sum is 35.

The square root of 639665 is about 799.7905975941. The cubic root of 639665 is about 86.1623488182.

The spelling of 639665 in words is "six hundred thirty-nine thousand, six hundred sixty-five".