639664391 has 2 divisors, whose sum is σ = 639664392. Its totient is φ = 639664390.

The previous prime is 639664379. The next prime is 639664409. The reversal of 639664391 is 193466936.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639664391 is a prime.

It is a super-2 number, since 2×639664391² = 818341066226801762, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (639664691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319832195 + 319832196.

It is an arithmetic number, because the mean of its divisors is an integer number (319832196).

Almost surely, 2^639664391 is an apocalyptic number.

639664391 is a deficient number, since it is larger than the sum of its proper divisors (1).

639664391 is an equidigital number, since it uses as much as digits as its factorization.

639664391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 629856, while the sum is 47.

The square root of 639664391 is about 25291.5873562732. The cubic root of 639664391 is about 861.6232147430.

The spelling of 639664391 in words is "six hundred thirty-nine million, six hundred sixty-four thousand, three hundred ninety-one".