19998191 has 4 divisors (see below), whose sum is σ = 20007912. Its totient is φ = 19988472.

The previous prime is 19998169. The next prime is 19998217. The reversal of 19998191 is 19189991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 19189991 = 17 ⋅1128823.

It is a cyclic number.

It is not a de Polignac number, because 19998191 - 2¹⁴ = 19981807 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19998151) 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, 425 + ... + 6338.

It is an arithmetic number, because the mean of its divisors is an integer number (5001978).

Almost surely, 2^19998191 is an apocalyptic number.

19998191 is a deficient number, since it is larger than the sum of its proper divisors (9721).

19998191 is an equidigital number, since it uses as much as digits as its factorization.

19998191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9720.

The product of its digits is 52488, while the sum is 47.

The square root of 19998191 is about 4471.9336980774. The cubic root of 19998191 is about 271.4335774436.

The spelling of 19998191 in words is "nineteen million, nine hundred ninety-eight thousand, one hundred ninety-one".