18821 has 8 divisors (see below), whose sum is σ = 21600. Its totient is φ = 16240.

The previous prime is 18803. The next prime is 18839. The reversal of 18821 is 12881.

It is an interprime number because it is at equal distance from previous prime (18803) and next prime (18839).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 18821 - 2⁶ = 18757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 15.

It is a nialpdrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 18793 and 18802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 290 + ... + 348.

It is an arithmetic number, because the mean of its divisors is an integer number (2700).

2¹⁸⁸²¹ is an apocalyptic number.

18821 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18821 is a deficient number, since it is larger than the sum of its proper divisors (2779).

18821 is a wasteful number, since it uses less digits than its factorization.

18821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99.

The product of its digits is 128, while the sum is 20.

The square root of 18821 is about 137.1896497554. The cubic root of 18821 is about 26.5999547741.

The spelling of 18821 in words is "eighteen thousand, eight hundred twenty-one".