109821 has 4 divisors (see below), whose sum is σ = 146432. Its totient is φ = 73212.

The previous prime is 109819. The next prime is 109829. The reversal of 109821 is 128901.

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, and also an emirpimes, since its reverse is a distinct semiprime: 128901 = 3 ⋅42967.

It is not a de Polignac number, because 109821 - 2¹ = 109819 is a prime.

It is a D-number.

It is a Duffinian number.

109821 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (109829) 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, 18301 + ... + 18306.

It is an arithmetic number, because the mean of its divisors is an integer number (36608).

2¹⁰⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

109821 is a deficient number, since it is larger than the sum of its proper divisors (36611).

109821 is an equidigital number, since it uses as much as digits as its factorization.

109821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36610.

The product of its (nonzero) digits is 144, while the sum is 21.

The square root of 109821 is about 331.3925165118. The cubic root of 109821 is about 47.8881946375. Note that the first 3 decimals are identical.

The spelling of 109821 in words is "one hundred nine thousand, eight hundred twenty-one".