21544665565 has 16 divisors (see below), whose sum is σ = 26264567808. Its totient is φ = 16962777216.

The previous prime is 21544665559. The next prime is 21544665577. The reversal of 21544665565 is 56556644512.

It is a cyclic number.

It is not a de Polignac number, because 21544665565 - 2¹³ = 21544657373 is a prime.

It is a super-2 number, since 2×21544665565² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 105252 + ... + 232738.

It is an arithmetic number, because the mean of its divisors is an integer number (1641535488).

Almost surely, 2^21544665565 is an apocalyptic number.

It is an amenable number.

21544665565 is a deficient number, since it is larger than the sum of its proper divisors (4719902243).

21544665565 is a wasteful number, since it uses less digits than its factorization.

21544665565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128028.

The product of its digits is 4320000, while the sum is 49.

The spelling of 21544665565 in words is "twenty-one billion, five hundred forty-four million, six hundred sixty-five thousand, five hundred sixty-five".