21545165 has 4 divisors (see below), whose sum is σ = 25854204. Its totient is φ = 17236128.

The previous prime is 21545149. The next prime is 21545179. The reversal of 21545165 is 56154512.

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 13053769 + 8491396 = 3613^2 + 2914^2 .

It is a cyclic number.

It is not a de Polignac number, because 21545165 - 2⁴ = 21545149 is a prime.

It is a Duffinian number.

It is a congruent number.

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, 2154512 + ... + 2154521.

It is an arithmetic number, because the mean of its divisors is an integer number (6463551).

Almost surely, 2^21545165 is an apocalyptic number.

It is an amenable number.

21545165 is a deficient number, since it is larger than the sum of its proper divisors (4309039).

21545165 is an equidigital number, since it uses as much as digits as its factorization.

21545165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4309038.

The product of its digits is 6000, while the sum is 29.

The square root of 21545165 is about 4641.6769598928. The cubic root of 21545165 is about 278.2594622307.

Adding to 21545165 its reverse (56154512), we get a palindrome (77699677).

The spelling of 21545165 in words is "twenty-one million, five hundred forty-five thousand, one hundred sixty-five".