19988891 has 4 divisors (see below), whose sum is σ = 21526512. Its totient is φ = 18451272.

The previous prime is 19988873. The next prime is 19988951. The reversal of 19988891 is 19888991.

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 19988891 - 2⁶ = 19988827 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19988291) 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, 768791 + ... + 768816.

It is an arithmetic number, because the mean of its divisors is an integer number (5381628).

Almost surely, 2^19988891 is an apocalyptic number.

19988891 is a deficient number, since it is larger than the sum of its proper divisors (1537621).

19988891 is a wasteful number, since it uses less digits than its factorization.

19988891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1537620.

The product of its digits is 373248, while the sum is 53.

The square root of 19988891 is about 4470.8937585230. The cubic root of 19988891 is about 271.3914949093.

The spelling of 19988891 in words is "nineteen million, nine hundred eighty-eight thousand, eight hundred ninety-one".