638691 has 4 divisors (see below), whose sum is σ = 851592. Its totient is φ = 425792.

The previous prime is 638689. The next prime is 638699. The reversal of 638691 is 196836.

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 638691 - 2¹ = 638689 is a prime.

It is a D-number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 638691.

It is not an unprimeable number, because it can be changed into a prime (638699) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106446 + ... + 106451.

It is an arithmetic number, because the mean of its divisors is an integer number (212898).

2⁶³⁸⁶⁹¹ is an apocalyptic number.

638691 is a deficient number, since it is larger than the sum of its proper divisors (212901).

638691 is a wasteful number, since it uses less digits than its factorization.

638691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212900.

The product of its digits is 7776, while the sum is 33.

The square root of 638691 is about 799.1814562413. The cubic root of 638691 is about 86.1185942701.

The spelling of 638691 in words is "six hundred thirty-eight thousand, six hundred ninety-one".