638685813 has 8 divisors (see below), whose sum is σ = 853422208. Its totient is φ = 424869984.

The previous prime is 638685793. The next prime is 638685841. The reversal of 638685813 is 318586836.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 638685813 - 2¹² = 638681717 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 (638685013) 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 7 ways as a sum of consecutive naturals, for example, 228520 + ... + 231297.

It is an arithmetic number, because the mean of its divisors is an integer number (106677776).

Almost surely, 2^638685813 is an apocalyptic number.

It is an amenable number.

638685813 is a deficient number, since it is larger than the sum of its proper divisors (214736395).

638685813 is a wasteful number, since it uses less digits than its factorization.

638685813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 460283.

The product of its digits is 829440, while the sum is 48.

The square root of 638685813 is about 25272.2340326296. The cubic root of 638685813 is about 861.1836113788.

The spelling of 638685813 in words is "six hundred thirty-eight million, six hundred eighty-five thousand, eight hundred thirteen".