639531391 has 2 divisors, whose sum is σ = 639531392. Its totient is φ = 639531390.

The previous prime is 639531371. The next prime is 639531401. The reversal of 639531391 is 193135936.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 639531391 - 2⁵ = 639531359 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (639531301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319765695 + 319765696.

It is an arithmetic number, because the mean of its divisors is an integer number (319765696).

Almost surely, 2^639531391 is an apocalyptic number.

639531391 is a deficient number, since it is larger than the sum of its proper divisors (1).

639531391 is an equidigital number, since it uses as much as digits as its factorization.

639531391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 65610, while the sum is 40.

The square root of 639531391 is about 25288.9578867932. The cubic root of 639531391 is about 861.5634939309.

The spelling of 639531391 in words is "six hundred thirty-nine million, five hundred thirty-one thousand, three hundred ninety-one".