18331921 has 4 divisors (see below), whose sum is σ = 18374692. Its totient is φ = 18289152.

The previous prime is 18331913. The next prime is 18331939. The reversal of 18331921 is 12913381.

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 8346321 + 9985600 = 2889^2 + 3160^2 .

It is a cyclic number.

It is not a de Polignac number, because 18331921 - 2³ = 18331913 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 18331921.

It is not an unprimeable number, because it can be changed into a prime (18331981) 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, 20736 + ... + 21601.

It is an arithmetic number, because the mean of its divisors is an integer number (4593673).

Almost surely, 2^18331921 is an apocalyptic number.

It is an amenable number.

18331921 is a deficient number, since it is larger than the sum of its proper divisors (42771).

18331921 is an equidigital number, since it uses as much as digits as its factorization.

18331921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42770.

The product of its digits is 1296, while the sum is 28.

The square root of 18331921 is about 4281.5792647106. The cubic root of 18331921 is about 263.6752252409.

The spelling of 18331921 in words is "eighteen million, three hundred thirty-one thousand, nine hundred twenty-one".