638453787821 has 4 divisors (see below), whose sum is σ = 640262439132. Its totient is φ = 636645136512.

The previous prime is 638453787809. The next prime is 638453787893. The reversal of 638453787821 is 128787354836.

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 449689606921 + 188764180900 = 670589^2 + 434470^2 .

It is a cyclic number.

It is not a de Polignac number, because 638453787821 - 2¹⁰ = 638453786797 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 (638453787121) 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, 904325126 + ... + 904325831.

It is an arithmetic number, because the mean of its divisors is an integer number (160065609783).

Almost surely, 2^638453787821 is an apocalyptic number.

It is an amenable number.

638453787821 is a deficient number, since it is larger than the sum of its proper divisors (1808651311).

638453787821 is a wasteful number, since it uses less digits than its factorization.

638453787821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1808651310.

The product of its digits is 54190080, while the sum is 62.

The spelling of 638453787821 in words is "six hundred thirty-eight billion, four hundred fifty-three million, seven hundred eighty-seven thousand, eight hundred twenty-one".