639731 has 2 divisors, whose sum is σ = 639732. Its totient is φ = 639730.

The previous prime is 639719. The next prime is 639739. The reversal of 639731 is 137936.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639731 is a prime.

It is a super-2 number, since 2×639731² = 818511504722, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 639694 and 639703.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 639731.

It is not a weakly prime, because it can be changed into another prime (639739) 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 as a sum of consecutive naturals, namely, 319865 + 319866.

It is an arithmetic number, because the mean of its divisors is an integer number (319866).

2⁶³⁹⁷³¹ is an apocalyptic number.

639731 is a deficient number, since it is larger than the sum of its proper divisors (1).

639731 is an equidigital number, since it uses as much as digits as its factorization.

639731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3402, while the sum is 29.

The square root of 639731 is about 799.8318573300. The cubic root of 639731 is about 86.1653120982.

The spelling of 639731 in words is "six hundred thirty-nine thousand, seven hundred thirty-one".