639526991 has 4 divisors (see below), whose sum is σ = 651593592. Its totient is φ = 627460392.

The previous prime is 639526969. The next prime is 639526997. The reversal of 639526991 is 199625936.

639526991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 639526991 - 2¹⁰ = 639525967 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639526997) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6033221 + ... + 6033326.

It is an arithmetic number, because the mean of its divisors is an integer number (162898398).

Almost surely, 2^639526991 is an apocalyptic number.

639526991 is a deficient number, since it is larger than the sum of its proper divisors (12066601).

639526991 is a wasteful number, since it uses less digits than its factorization.

639526991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12066600.

The product of its digits is 787320, while the sum is 50.

The square root of 639526991 is about 25288.8708921533. The cubic root of 639526991 is about 861.5615180633.

The spelling of 639526991 in words is "six hundred thirty-nine million, five hundred twenty-six thousand, nine hundred ninety-one".