21801 has 12 divisors (see below), whose sum is σ = 32208. Its totient is φ = 13104.

The previous prime is 21799. The next prime is 21803. The reversal of 21801 is 10812.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21799) and next prime (21803).

It is not a de Polignac number, because 21801 - 2¹ = 21799 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 486 + ... + 528.

It is an arithmetic number, because the mean of its divisors is an integer number (2684).

2²¹⁸⁰¹ is an apocalyptic number.

It is an amenable number.

21801 is a deficient number, since it is larger than the sum of its proper divisors (10407).

21801 is a wasteful number, since it uses less digits than its factorization.

21801 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72 (or 59 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 21801 is about 147.6516169908. The cubic root of 21801 is about 27.9356515500.

The spelling of 21801 in words is "twenty-one thousand, eight hundred one".