639128939 has 2 divisors, whose sum is σ = 639128940. Its totient is φ = 639128938.

The previous prime is 639128929. The next prime is 639128977. The reversal of 639128939 is 939821936.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 639128939 - 2⁸ = 639128683 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (639128929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319564469 + 319564470.

It is an arithmetic number, because the mean of its divisors is an integer number (319564470).

Almost surely, 2^639128939 is an apocalyptic number.

639128939 is a deficient number, since it is larger than the sum of its proper divisors (1).

639128939 is an equidigital number, since it uses as much as digits as its factorization.

639128939 is an evil number, because the sum of its binary digits is even.

The product of its digits is 629856, while the sum is 50.

The square root of 639128939 is about 25280.9995648906. Note that the first 3 decimals coincide. The cubic root of 639128939 is about 861.3827309979.

The spelling of 639128939 in words is "six hundred thirty-nine million, one hundred twenty-eight thousand, nine hundred thirty-nine".