639851 has 2 divisors, whose sum is σ = 639852. Its totient is φ = 639850.

The previous prime is 639839. The next prime is 639853. The reversal of 639851 is 158936.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639851 is a prime.

It is a Sophie Germain prime.

Together with 639853, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (639853) 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, 319925 + 319926.

It is an arithmetic number, because the mean of its divisors is an integer number (319926).

2⁶³⁹⁸⁵¹ is an apocalyptic number.

639851 is a deficient number, since it is larger than the sum of its proper divisors (1).

639851 is an equidigital number, since it uses as much as digits as its factorization.

639851 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 32.

The square root of 639851 is about 799.9068695792. The cubic root of 639851 is about 86.1706993579.

The spelling of 639851 in words is "six hundred thirty-nine thousand, eight hundred fifty-one".