18705991 has 4 divisors (see below), whose sum is σ = 18775800. Its totient is φ = 18636184.

The previous prime is 18705983. The next prime is 18706003. The reversal of 18705991 is 19950781.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19950781 = 197 ⋅101273.

It is a cyclic number.

It is not a de Polignac number, because 18705991 - 2³ = 18705983 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 (18705901) 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, 34501 + ... + 35038.

It is an arithmetic number, because the mean of its divisors is an integer number (4693950).

Almost surely, 2^18705991 is an apocalyptic number.

18705991 is a deficient number, since it is larger than the sum of its proper divisors (69809).

18705991 is an equidigital number, since it uses as much as digits as its factorization.

18705991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69808.

The product of its (nonzero) digits is 22680, while the sum is 40.

The square root of 18705991 is about 4325.0423119318. The cubic root of 18705991 is about 265.4566281709.

The spelling of 18705991 in words is "eighteen million, seven hundred five thousand, nine hundred ninety-one".