21355 has 4 divisors (see below), whose sum is σ = 25632. Its totient is φ = 17080.

The previous prime is 21347. The next prime is 21377. The reversal of 21355 is 55312.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21355 - 2³ = 21347 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2131 + ... + 2140.

It is an arithmetic number, because the mean of its divisors is an integer number (6408).

2²¹³⁵⁵ is an apocalyptic number.

21355 is a deficient number, since it is larger than the sum of its proper divisors (4277).

21355 is an equidigital number, since it uses as much as digits as its factorization.

21355 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4276.

The product of its digits is 150, while the sum is 16.

The square root of 21355 is about 146.1335006082. The cubic root of 21355 is about 27.7438370644.

Adding to 21355 its reverse (55312), we get a palindrome (76667).

The spelling of 21355 in words is "twenty-one thousand, three hundred fifty-five".