21973 has 8 divisors (see below), whose sum is σ = 26048. Its totient is φ = 18144.

The previous prime is 21961. The next prime is 21977. The reversal of 21973 is 37912.

21973 is nontrivially palindromic in base 2 and base 8.

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

It is not a de Polignac number, because 21973 - 2¹³ = 13781 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11 and base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21977) 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, 265 + ... + 337.

It is an arithmetic number, because the mean of its divisors is an integer number (3256).

2²¹⁹⁷³ is an apocalyptic number.

It is an amenable number.

21973 is a deficient number, since it is larger than the sum of its proper divisors (4075).

21973 is an equidigital number, since it uses as much as digits as its factorization.

21973 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123.

The product of its digits is 378, while the sum is 22.

The square root of 21973 is about 148.2329248177. The cubic root of 21973 is about 28.0089257258.

It can be divided in two parts, 219 and 73, that added together give a palindrome (292).

The spelling of 21973 in words is "twenty-one thousand, nine hundred seventy-three".