21597 has 8 divisors (see below), whose sum is σ = 30144. Its totient is φ = 13728.

The previous prime is 21589. The next prime is 21599. The reversal of 21597 is 79512.

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

It is not a de Polignac number, because 21597 - 2³ = 21589 is a prime.

21597 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21599) 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, 88 + ... + 225.

It is an arithmetic number, because the mean of its divisors is an integer number (3768).

2²¹⁵⁹⁷ is an apocalyptic number.

It is an amenable number.

21597 is a deficient number, since it is larger than the sum of its proper divisors (8547).

21597 is a wasteful number, since it uses less digits than its factorization.

21597 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 339.

The product of its digits is 630, while the sum is 24.

The square root of 21597 is about 146.9591780053. The cubic root of 21597 is about 27.8482436117.

The spelling of 21597 in words is "twenty-one thousand, five hundred ninety-seven".