19997391 has 4 divisors (see below), whose sum is σ = 26663192. Its totient is φ = 13331592.

The previous prime is 19997357. The next prime is 19997399. The reversal of 19997391 is 19379991.

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

It is not a de Polignac number, because 19997391 - 2¹¹ = 19995343 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 19997391.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19997399) 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, 3332896 + ... + 3332901.

It is an arithmetic number, because the mean of its divisors is an integer number (6665798).

Almost surely, 2^19997391 is an apocalyptic number.

19997391 is a deficient number, since it is larger than the sum of its proper divisors (6665801).

19997391 is an equidigital number, since it uses as much as digits as its factorization.

19997391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6665800.

The product of its digits is 137781, while the sum is 48.

The square root of 19997391 is about 4471.8442504184. The cubic root of 19997391 is about 271.4299579536.

The spelling of 19997391 in words is "nineteen million, nine hundred ninety-seven thousand, three hundred ninety-one".