638995691 has 4 divisors (see below), whose sum is σ = 652591392. Its totient is φ = 625399992.

The previous prime is 638995681. The next prime is 638995699. The reversal of 638995691 is 196599836.

638995691 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 638995691 - 2⁶ = 638995627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638995699) 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, 6797780 + ... + 6797873.

It is an arithmetic number, because the mean of its divisors is an integer number (163147848).

Almost surely, 2^638995691 is an apocalyptic number.

638995691 is a deficient number, since it is larger than the sum of its proper divisors (13595701).

638995691 is a wasteful number, since it uses less digits than its factorization.

638995691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13595700.

The product of its digits is 3149280, while the sum is 56.

The square root of 638995691 is about 25278.3640886826. The cubic root of 638995691 is about 861.3228654025.

The spelling of 638995691 in words is "six hundred thirty-eight million, nine hundred ninety-five thousand, six hundred ninety-one".