21797 has 4 divisors (see below), whose sum is σ = 22176. Its totient is φ = 21420.

The previous prime is 21787. The next prime is 21799. The reversal of 21797 is 79712.

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 21797 - 2¹⁰ = 20773 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21799) 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 3 ways as a sum of consecutive naturals, for example, 83 + ... + 224.

It is an arithmetic number, because the mean of its divisors is an integer number (5544).

2²¹⁷⁹⁷ is an apocalyptic number.

It is an amenable number.

21797 is a deficient number, since it is larger than the sum of its proper divisors (379).

21797 is an equidigital number, since it uses as much as digits as its factorization.

21797 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 378.

The product of its digits is 882, while the sum is 26.

The square root of 21797 is about 147.6380709709. The cubic root of 21797 is about 27.9339429214.

It can be divided in two parts, 21 and 797, that added together give a palindrome (818).

The spelling of 21797 in words is "twenty-one thousand, seven hundred ninety-seven".