21265 has 4 divisors (see below), whose sum is σ = 25524. Its totient is φ = 17008.

The previous prime is 21247. The next prime is 21269. The reversal of 21265 is 56212.

It is a happy number.

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 4624 + 16641 = 68^2 + 129^2 .

It is a cyclic number.

It is not a de Polignac number, because 21265 - 2⁹ = 20753 is a prime.

It is a Duffinian number.

It is a plaindrome in base 7.

It is a nialpdrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21269) 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, 2122 + ... + 2131.

It is an arithmetic number, because the mean of its divisors is an integer number (6381).

2²¹²⁶⁵ is an apocalyptic number.

It is an amenable number.

21265 is a deficient number, since it is larger than the sum of its proper divisors (4259).

21265 is an equidigital number, since it uses as much as digits as its factorization.

21265 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4258.

The product of its digits is 120, while the sum is 16.

The square root of 21265 is about 145.8252378705. The cubic root of 21265 is about 27.7048069959.

Adding to 21265 its reverse (56212), we get a palindrome (77477).

It can be divided in two parts, 21 and 265, that multiplied together give a triangular number (5565 = T₁₀₅).

The spelling of 21265 in words is "twenty-one thousand, two hundred sixty-five".