21709306665 has 64 divisors (see below), whose sum is σ = 39883898880. Its totient is φ = 11192264640.

The previous prime is 21709306643. The next prime is 21709306669. The reversal of 21709306665 is 56660390712.

It is not a de Polignac number, because 21709306665 - 2⁷ = 21709306537 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 21709306665.

It is not an unprimeable number, because it can be changed into a prime (21709306669) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 4613704 + ... + 4618406.

It is an arithmetic number, because the mean of its divisors is an integer number (623185920).

Almost surely, 2^21709306665 is an apocalyptic number.

It is an amenable number.

21709306665 is a deficient number, since it is larger than the sum of its proper divisors (18174592215).

21709306665 is a wasteful number, since it uses less digits than its factorization.

21709306665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5851 (or 5845 counting only the distinct ones).

The product of its (nonzero) digits is 408240, while the sum is 45.

The spelling of 21709306665 in words is "twenty-one billion, seven hundred nine million, three hundred six thousand, six hundred sixty-five".