21288065 has 4 divisors (see below), whose sum is σ = 25545684. Its totient is φ = 17030448.

The previous prime is 21288049. The next prime is 21288067. The reversal of 21288065 is 56088212.

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 5740816 + 15547249 = 2396^2 + 3943^2 .

It is a cyclic number.

It is not a de Polignac number, because 21288065 - 2⁴ = 21288049 is a prime.

It is a super-2 number, since 2×21288065² = 906363422888450, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21288067) 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, 2128802 + ... + 2128811.

It is an arithmetic number, because the mean of its divisors is an integer number (6386421).

Almost surely, 2^21288065 is an apocalyptic number.

It is an amenable number.

21288065 is a deficient number, since it is larger than the sum of its proper divisors (4257619).

21288065 is an equidigital number, since it uses as much as digits as its factorization.

21288065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4257618.

The product of its (nonzero) digits is 7680, while the sum is 32.

The square root of 21288065 is about 4613.8991102971. The cubic root of 21288065 is about 277.1482001384.

The spelling of 21288065 in words is "twenty-one million, two hundred eighty-eight thousand, sixty-five".