21021606565 has 24 divisors (see below), whose sum is σ = 26151154848. Its totient is φ = 16221616320.

The previous prime is 21021606511. The next prime is 21021606577. The reversal of 21021606565 is 56560612012.

It is not a de Polignac number, because 21021606565 - 2¹¹ = 21021604517 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21021606565.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6234330 + ... + 6237700.

It is an arithmetic number, because the mean of its divisors is an integer number (1089631452).

Almost surely, 2^21021606565 is an apocalyptic number.

It is an amenable number.

21021606565 is a deficient number, since it is larger than the sum of its proper divisors (5129548283).

21021606565 is a wasteful number, since it uses less digits than its factorization.

21021606565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4917 (or 4888 counting only the distinct ones).

The product of its (nonzero) digits is 21600, while the sum is 34.

The spelling of 21021606565 in words is "twenty-one billion, twenty-one million, six hundred six thousand, five hundred sixty-five".