18001821 has 16 divisors (see below), whose sum is σ = 25033536. Its totient is φ = 11496576.

The previous prime is 18001817. The next prime is 18001843. The reversal of 18001821 is 12810081.

It is not a de Polignac number, because 18001821 - 2² = 18001817 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18001811) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5521 + ... + 8153.

It is an arithmetic number, because the mean of its divisors is an integer number (1564596).

Almost surely, 2^18001821 is an apocalyptic number.

It is an amenable number.

18001821 is a deficient number, since it is larger than the sum of its proper divisors (7031715).

18001821 is a wasteful number, since it uses less digits than its factorization.

18001821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2732.

The product of its (nonzero) digits is 128, while the sum is 21.

The square root of 18001821 is about 4242.8552885999. The cubic root of 18001821 is about 262.0829768452.

The spelling of 18001821 in words is "eighteen million, one thousand, eight hundred twenty-one".