638865856637 has 4 divisors (see below), whose sum is σ = 643153547100. Its totient is φ = 634578166176.

The previous prime is 638865856511. The next prime is 638865856639. The reversal of 638865856637 is 736658568836.

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 330278940601 + 308586916036 = 574699^2 + 555506^2 .

It is a cyclic number.

It is not a de Polignac number, because 638865856637 - 2¹⁴ = 638865840253 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 (638865856639) 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, 2143845008 + ... + 2143845305.

It is an arithmetic number, because the mean of its divisors is an integer number (160788386775).

Almost surely, 2^638865856637 is an apocalyptic number.

It is an amenable number.

638865856637 is a deficient number, since it is larger than the sum of its proper divisors (4287690463).

638865856637 is a wasteful number, since it uses less digits than its factorization.

638865856637 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4287690462.

The product of its digits is 1045094400, while the sum is 71.

The spelling of 638865856637 in words is "six hundred thirty-eight billion, eight hundred sixty-five million, eight hundred fifty-six thousand, six hundred thirty-seven".