21253 has 4 divisors (see below), whose sum is σ = 21708. Its totient is φ = 20800.

The previous prime is 21247. The next prime is 21269. The reversal of 21253 is 35212.

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 19044 + 2209 = 138^2 + 47^2 .

It is a cyclic number.

It is not a de Polignac number, because 21253 - 2⁵ = 21221 is a prime.

It is a Smith number, since the sum of its digits (13) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

21253 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21283) 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, 148 + ... + 253.

It is an arithmetic number, because the mean of its divisors is an integer number (5427).

2²¹²⁵³ is an apocalyptic number.

It is an amenable number.

21253 is a deficient number, since it is larger than the sum of its proper divisors (455).

21253 is an equidigital number, since it uses as much as digits as its factorization.

21253 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 454.

The product of its digits is 60, while the sum is 13.

The square root of 21253 is about 145.7840869231. The cubic root of 21253 is about 27.6995946714.

Adding to 21253 its reverse (35212), we get a palindrome (56465).

It can be divided in two parts, 212 and 53, that multiplied together give a square (11236 = 106²).

The spelling of 21253 in words is "twenty-one thousand, two hundred fifty-three".