21053 has 4 divisors (see below), whose sum is σ = 21660. Its totient is φ = 20448.

The previous prime is 21031. The next prime is 21059. The reversal of 21053 is 35012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11449 + 9604 = 107^2 + 98^2 .

It is a cyclic number.

It is not a de Polignac number, because 21053 - 2¹⁰ = 20029 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21059) 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, 248 + ... + 321.

It is an arithmetic number, because the mean of its divisors is an integer number (5415).

2²¹⁰⁵³ is an apocalyptic number.

It is an amenable number.

21053 is a deficient number, since it is larger than the sum of its proper divisors (607).

21053 is an equidigital number, since it uses as much as digits as its factorization.

21053 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 606.

The product of its (nonzero) digits is 30, while the sum is 11.

The square root of 21053 is about 145.0965195999. The cubic root of 21053 is about 27.6124322623.

Adding to 21053 its reverse (35012), we get a palindrome (56065).

The spelling of 21053 in words is "twenty-one thousand, fifty-three".