21265765 has 4 divisors (see below), whose sum is σ = 25518924. Its totient is φ = 17012608.

The previous prime is 21265747. The next prime is 21265771. The reversal of 21265765 is 56756212.

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 15729156 + 5536609 = 3966^2 + 2353^2 .

It is a cyclic number.

It is not a de Polignac number, because 21265765 - 2⁹ = 21265253 is a prime.

It is a super-2 number, since 2×21265765² = 904465522070450, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21265765.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2126572 + ... + 2126581.

It is an arithmetic number, because the mean of its divisors is an integer number (6379731).

Almost surely, 2^21265765 is an apocalyptic number.

It is an amenable number.

21265765 is a deficient number, since it is larger than the sum of its proper divisors (4253159).

21265765 is an equidigital number, since it uses as much as digits as its factorization.

21265765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4253158.

The product of its digits is 25200, while the sum is 34.

The square root of 21265765 is about 4611.4818659516. The cubic root of 21265765 is about 277.0513921510.

The spelling of 21265765 in words is "twenty-one million, two hundred sixty-five thousand, seven hundred sixty-five".