18921818 has 4 divisors (see below), whose sum is σ = 28382730. Its totient is φ = 9460908.

The previous prime is 18921817. The next prime is 18921829. The reversal of 18921818 is 81812981.

It is a happy number.

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

It can be written as a sum of positive squares in only one way, i.e., 15547249 + 3374569 = 3943^2 + 1837^2 .

It is an alternating number because its digits alternate between odd and even.

It is not an unprimeable number, because it can be changed into a prime (18921817) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4730453 + ... + 4730456.

Almost surely, 2^18921818 is an apocalyptic number.

18921818 is a deficient number, since it is larger than the sum of its proper divisors (9460912).

18921818 is an equidigital number, since it uses as much as digits as its factorization.

18921818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9460911.

The product of its digits is 9216, while the sum is 38.

The square root of 18921818 is about 4349.9216084891. The cubic root of 18921818 is about 266.4736599931.

The spelling of 18921818 in words is "eighteen million, nine hundred twenty-one thousand, eight hundred eighteen".