638443220018 has 6 divisors (see below), whose sum is σ = 957666525021. Its totient is φ = 319221045012.

The previous prime is 638443220017. The next prime is 638443220029. The reversal of 638443220018 is 810022344836.

It can be written as a sum of positive squares in 2 ways, for example, as 325227262369 + 313215957649 = 570287^2 + 559657^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=564997.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638443220017) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 847496 + ... + 1412492.

Almost surely, 2^638443220018 is an apocalyptic number.

638443220018 is a deficient number, since it is larger than the sum of its proper divisors (319223305003).

638443220018 is an frugal number, since it uses more digits than its factorization.

638443220018 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1129996 (or 564999 counting only the distinct ones).

The product of its (nonzero) digits is 221184, while the sum is 41.

The spelling of 638443220018 in words is "six hundred thirty-eight billion, four hundred forty-three million, two hundred twenty thousand, eighteen".