21201565 has 24 divisors (see below), whose sum is σ = 32290272. Its totient is φ = 13214880.

The previous prime is 21201563. The next prime is 21201569. The reversal of 21201565 is 56510212.

It is not a de Polignac number, because 21201565 - 2¹ = 21201563 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21201563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1239 + ... + 6628.

It is an arithmetic number, because the mean of its divisors is an integer number (1345428).

Almost surely, 2^21201565 is an apocalyptic number.

It is an amenable number.

21201565 is a deficient number, since it is larger than the sum of its proper divisors (11088707).

21201565 is a wasteful number, since it uses less digits than its factorization.

21201565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7897 (or 7890 counting only the distinct ones).

The product of its (nonzero) digits is 600, while the sum is 22.

The square root of 21201565 is about 4604.5157182922. The cubic root of 21201565 is about 276.7723109074.

Adding to 21201565 its reverse (56510212), we get a palindrome (77711777).

The spelling of 21201565 in words is "twenty-one million, two hundred one thousand, five hundred sixty-five".