639875921 has 2 divisors, whose sum is σ = 639875922. Its totient is φ = 639875920.

The previous prime is 639875851. The next prime is 639875953. The reversal of 639875921 is 129578936.

639875921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 447914896 + 191961025 = 21164^2 + 13855^2 .

It is a cyclic number.

It is not a de Polignac number, because 639875921 - 2¹⁰ = 639874897 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 639875921.

It is not a weakly prime, because it can be changed into another prime (639875321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319937960 + 319937961.

It is an arithmetic number, because the mean of its divisors is an integer number (319937961).

Almost surely, 2^639875921 is an apocalyptic number.

It is an amenable number.

639875921 is a deficient number, since it is larger than the sum of its proper divisors (1).

639875921 is an equidigital number, since it uses as much as digits as its factorization.

639875921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 816480, while the sum is 50.

The square root of 639875921 is about 25295.7688359140. The cubic root of 639875921 is about 861.7181807254.

The spelling of 639875921 in words is "six hundred thirty-nine million, eight hundred seventy-five thousand, nine hundred twenty-one".