638844661787 has 4 divisors (see below), whose sum is σ = 638856954960. Its totient is φ = 638832368616.

The previous prime is 638844661783. The next prime is 638844661813. The reversal of 638844661787 is 787166448836.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 638844661787 - 2² = 638844661783 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638844661783) 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, 6068303 + ... + 6172680.

It is an arithmetic number, because the mean of its divisors is an integer number (159714238740).

Almost surely, 2^638844661787 is an apocalyptic number.

638844661787 is a deficient number, since it is larger than the sum of its proper divisors (12293173).

638844661787 is a wasteful number, since it uses less digits than its factorization.

638844661787 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12293172.

The product of its digits is 260112384, while the sum is 68.

The spelling of 638844661787 in words is "six hundred thirty-eight billion, eight hundred forty-four million, six hundred sixty-one thousand, seven hundred eighty-seven".