21387265 has 4 divisors (see below), whose sum is σ = 25664724. Its totient is φ = 17109808.

The previous prime is 21387257. The next prime is 21387277. The reversal of 21387265 is 56278312.

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 11943936 + 9443329 = 3456^2 + 3073^2 .

It is a cyclic number.

It is not a de Polignac number, because 21387265 - 2³ = 21387257 is a prime.

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 21387265.

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, 2138722 + ... + 2138731.

It is an arithmetic number, because the mean of its divisors is an integer number (6416181).

Almost surely, 2^21387265 is an apocalyptic number.

It is an amenable number.

21387265 is a deficient number, since it is larger than the sum of its proper divisors (4277459).

21387265 is an equidigital number, since it uses as much as digits as its factorization.

21387265 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4277458.

The product of its digits is 20160, while the sum is 34.

The square root of 21387265 is about 4624.6367424912. The cubic root of 21387265 is about 277.5780263774.

It can be divided in two parts, 213 and 87265, that added together give a palindrome (87478).

The spelling of 21387265 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred sixty-five".