21553165 has 4 divisors (see below), whose sum is σ = 25863804. Its totient is φ = 17242528.

The previous prime is 21553157. The next prime is 21553183. The reversal of 21553165 is 56135512.

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 11737476 + 9815689 = 3426^2 + 3133^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553165 - 2³ = 21553157 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, 2155312 + ... + 2155321.

It is an arithmetic number, because the mean of its divisors is an integer number (6465951).

Almost surely, 2^21553165 is an apocalyptic number.

It is an amenable number.

21553165 is a deficient number, since it is larger than the sum of its proper divisors (4310639).

21553165 is an equidigital number, since it uses as much as digits as its factorization.

21553165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4310638.

The product of its digits is 4500, while the sum is 28.

The square root of 21553165 is about 4642.5386374267. The cubic root of 21553165 is about 278.2938984214.

Adding to 21553165 its reverse (56135512), we get a palindrome (77688677).

The spelling of 21553165 in words is "twenty-one million, five hundred fifty-three thousand, one hundred sixty-five".