18431921 has 4 divisors (see below), whose sum is σ = 18508644. Its totient is φ = 18355200.

The previous prime is 18431879. The next prime is 18431923. The reversal of 18431921 is 12913481.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4999696 + 13432225 = 2236^2 + 3665^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18431921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18431923) 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, 38000 + ... + 38481.

It is an arithmetic number, because the mean of its divisors is an integer number (4627161).

Almost surely, 2^18431921 is an apocalyptic number.

It is an amenable number.

18431921 is a deficient number, since it is larger than the sum of its proper divisors (76723).

18431921 is an equidigital number, since it uses as much as digits as its factorization.

18431921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76722.

The product of its digits is 1728, while the sum is 29.

The square root of 18431921 is about 4293.2413163017. The cubic root of 18431921 is about 264.1538025206.

The spelling of 18431921 in words is "eighteen million, four hundred thirty-one thousand, nine hundred twenty-one".