21320165 has 4 divisors (see below), whose sum is σ = 25584204. Its totient is φ = 17056128.

The previous prime is 21320107. The next prime is 21320183. The reversal of 21320165 is 56102312.

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 6466849 + 14853316 = 2543^2 + 3854^2 .

It is a cyclic number.

It is not a de Polignac number, because 21320165 - 2¹⁴ = 21303781 is a prime.

It is a Duffinian number.

It is a Curzon 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, 2132012 + ... + 2132021.

It is an arithmetic number, because the mean of its divisors is an integer number (6396051).

Almost surely, 2^21320165 is an apocalyptic number.

It is an amenable number.

21320165 is a deficient number, since it is larger than the sum of its proper divisors (4264039).

21320165 is an equidigital number, since it uses as much as digits as its factorization.

21320165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4264038.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21320165 is about 4617.3764195699. The cubic root of 21320165 is about 277.2874329174.

Adding to 21320165 its reverse (56102312), we get a palindrome (77422477).

The spelling of 21320165 in words is "twenty-one million, three hundred twenty thousand, one hundred sixty-five".