21353 has 4 divisors (see below), whose sum is σ = 21648. Its totient is φ = 21060.

The previous prime is 21347. The next prime is 21377. The reversal of 21353 is 35312.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21353 - 2¹² = 17257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21313) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 50 + ... + 212.

It is an arithmetic number, because the mean of its divisors is an integer number (5412).

2²¹³⁵³ is an apocalyptic number.

It is an amenable number.

21353 is a deficient number, since it is larger than the sum of its proper divisors (295).

21353 is a wasteful number, since it uses less digits than its factorization.

21353 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294.

The product of its digits is 90, while the sum is 14.

The square root of 21353 is about 146.1266573901. The cubic root of 21353 is about 27.7429709221.

Adding to 21353 its reverse (35312), we get a palindrome (56665).

The spelling of 21353 in words is "twenty-one thousand, three hundred fifty-three".