638509891405 has 4 divisors (see below), whose sum is σ = 766211869692. Its totient is φ = 510807913120.

The previous prime is 638509891387. The next prime is 638509891447. The reversal of 638509891405 is 504198905836.

638509891405 = 565026² + 565027².

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 319255510729 + 319254380676 = 565027^2 + 565026^2 .

It is not a de Polignac number, because 638509891405 - 2²³ = 638501502797 is a prime.

It is a Smith number, since the sum of its digits (58) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 638509891405.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63850989136 + ... + 63850989145.

It is an arithmetic number, because the mean of its divisors is an integer number (191552967423).

Almost surely, 2^638509891405 is an apocalyptic number.

638509891405 is the 565027-th centered square number.

It is an amenable number.

638509891405 is a deficient number, since it is larger than the sum of its proper divisors (127701978287).

638509891405 is a wasteful number, since it uses less digits than its factorization.

638509891405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127701978286.

The product of its (nonzero) digits is 9331200, while the sum is 58.

The spelling of 638509891405 in words is "six hundred thirty-eight billion, five hundred nine million, eight hundred ninety-one thousand, four hundred five".