639751 has 4 divisors (see below), whose sum is σ = 731152. Its totient is φ = 548352.

The previous prime is 639739. The next prime is 639757. The reversal of 639751 is 157936.

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

It is not a de Polignac number, because 639751 - 2⁵ = 639719 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639757) 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, 45690 + ... + 45703.

It is an arithmetic number, because the mean of its divisors is an integer number (182788).

2⁶³⁹⁷⁵¹ is an apocalyptic number.

639751 is a deficient number, since it is larger than the sum of its proper divisors (91401).

639751 is an equidigital number, since it uses as much as digits as its factorization.

639751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91400.

The product of its digits is 5670, while the sum is 31.

The square root of 639751 is about 799.8443598601. The cubic root of 639751 is about 86.1662100216.

The spelling of 639751 in words is "six hundred thirty-nine thousand, seven hundred fifty-one".