638785621 has 4 divisors (see below), whose sum is σ = 638851212. Its totient is φ = 638720032.

The previous prime is 638785561. The next prime is 638785633. The reversal of 638785621 is 126587836.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 440370225 + 198415396 = 20985^2 + 14086^2 .

It is a cyclic number.

It is not a de Polignac number, because 638785621 - 2⁷ = 638785493 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 (638785321) 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, 14950 + ... + 38743.

It is an arithmetic number, because the mean of its divisors is an integer number (159712803).

Almost surely, 2^638785621 is an apocalyptic number.

It is an amenable number.

638785621 is a deficient number, since it is larger than the sum of its proper divisors (65591).

638785621 is a wasteful number, since it uses less digits than its factorization.

638785621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65590.

The product of its digits is 483840, while the sum is 46.

The square root of 638785621 is about 25274.2086127340. The cubic root of 638785621 is about 861.2284683519.

The spelling of 638785621 in words is "six hundred thirty-eight million, seven hundred eighty-five thousand, six hundred twenty-one".