638681 has 4 divisors (see below), whose sum is σ = 641700. Its totient is φ = 635664.

The previous prime is 638669. The next prime is 638689. The reversal of 638681 is 186836.

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

It can be written as a sum of positive squares in 2 ways, for example, as 512656 + 126025 = 716^2 + 355^2 .

It is a cyclic number.

It is not a de Polignac number, because 638681 - 2¹⁰ = 637657 is a prime.

It is a super-2 number, since 2×638681² = 815826839522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638689) 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, 1166 + ... + 1623.

It is an arithmetic number, because the mean of its divisors is an integer number (160425).

2⁶³⁸⁶⁸¹ is an apocalyptic number.

It is an amenable number.

638681 is a deficient number, since it is larger than the sum of its proper divisors (3019).

638681 is a wasteful number, since it uses less digits than its factorization.

638681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3018.

The product of its digits is 6912, while the sum is 32.

The square root of 638681 is about 799.1751998154. The cubic root of 638681 is about 86.1181448141.

The spelling of 638681 in words is "six hundred thirty-eight thousand, six hundred eighty-one".