21291 has 8 divisors (see below), whose sum is σ = 29184. Its totient is φ = 13800.

The previous prime is 21283. The next prime is 21313. The reversal of 21291 is 19212.

It is a happy number.

21291 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 21291 - 2³ = 21283 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21291.

It is not an unprimeable number, because it can be changed into a prime (21211) 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, 66 + ... + 216.

It is an arithmetic number, because the mean of its divisors is an integer number (3648).

2²¹²⁹¹ is an apocalyptic number.

21291 is a deficient number, since it is larger than the sum of its proper divisors (7893).

21291 is a wasteful number, since it uses less digits than its factorization.

21291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201.

The product of its digits is 36, while the sum is 15.

The square root of 21291 is about 145.9143584436. The cubic root of 21291 is about 27.7160936423.

It can be divided in two parts, 212 and 91, that added together give a palindrome (303).

The spelling of 21291 in words is "twenty-one thousand, two hundred ninety-one".