18987821 has 4 divisors (see below), whose sum is σ = 19987200. Its totient is φ = 17988444.

The previous prime is 18987803. The next prime is 18987853. The reversal of 18987821 is 12878981.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 18987821 - 2⁶ = 18987757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18981821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 499661 + ... + 499698.

It is an arithmetic number, because the mean of its divisors is an integer number (4996800).

Almost surely, 2^18987821 is an apocalyptic number.

It is an amenable number.

18987821 is a deficient number, since it is larger than the sum of its proper divisors (999379).

18987821 is an equidigital number, since it uses as much as digits as its factorization.

18987821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 999378.

The product of its digits is 64512, while the sum is 44.

The square root of 18987821 is about 4357.5016924839. The cubic root of 18987821 is about 266.7831378371.

The spelling of 18987821 in words is "eighteen million, nine hundred eighty-seven thousand, eight hundred twenty-one".