21565163221 has 16 divisors (see below), whose sum is σ = 26230898304. Its totient is φ = 17306947584.

The previous prime is 21565163209. The next prime is 21565163281. The reversal of 21565163221 is 12236156512.

It is a cyclic number.

It is not a de Polignac number, because 21565163221 - 2⁹ = 21565162709 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565163281) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 446515 + ... + 492448.

It is an arithmetic number, because the mean of its divisors is an integer number (1639431144).

Almost surely, 2^21565163221 is an apocalyptic number.

It is an amenable number.

21565163221 is a deficient number, since it is larger than the sum of its proper divisors (4665735083).

21565163221 is a wasteful number, since it uses less digits than its factorization.

21565163221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 939180.

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

It can be divided in two parts, 215651 and 63221, that added together give a palindrome (278872).

The spelling of 21565163221 in words is "twenty-one billion, five hundred sixty-five million, one hundred sixty-three thousand, two hundred twenty-one".