21201665 has 8 divisors (see below), whose sum is σ = 25800768. Its totient is φ = 16722160.

The previous prime is 21201647. The next prime is 21201673. The reversal of 21201665 is 56610212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21201665 - 2¹² = 21197569 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21201665.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29507 + ... + 30216.

It is an arithmetic number, because the mean of its divisors is an integer number (3225096).

Almost surely, 2^21201665 is an apocalyptic number.

It is an amenable number.

21201665 is a deficient number, since it is larger than the sum of its proper divisors (4599103).

21201665 is an equidigital number, since it uses as much as digits as its factorization.

21201665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59799.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21201665 is about 4604.5265771847. The cubic root of 21201665 is about 276.7727460511.

Adding to 21201665 its reverse (56610212), we get a palindrome (77811877).

The spelling of 21201665 in words is "twenty-one million, two hundred one thousand, six hundred sixty-five".