1638723888891 has 12 divisors (see below), whose sum is σ = 2375409739768. Its totient is φ = 1088622228384.

The previous prime is 1638723888881. The next prime is 1638723888913. The reversal of 1638723888891 is 1988883278361.

1638723888891 is a `hidden beast` number, since 1 + 6 + 3 + 87 + 2 + 388 + 88 + 91 = 666.

It is not a de Polignac number, because 1638723888891 - 2⁶ = 1638723888827 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1638723888871) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 321694330 + ... + 321699423.

Almost surely, 2^{1638723888891} is an apocalyptic number.

1638723888891 is a deficient number, since it is larger than the sum of its proper divisors (736685850877).

1638723888891 is a wasteful number, since it uses less digits than its factorization.

1638723888891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 643394042 (or 643394039 counting only the distinct ones).

The product of its digits is 222953472, while the sum is 72.

The spelling of 1638723888891 in words is "one trillion, six hundred thirty-eight billion, seven hundred twenty-three million, eight hundred eighty-eight thousand, eight hundred ninety-one".