21321137565 has 96 divisors (see below), whose sum is σ = 47879220480. Its totient is φ = 8523491328.

The previous prime is 21321137549. The next prime is 21321137573. The reversal of 21321137565 is 56573112312.

21321137565 is a `hidden beast` number, since 2 + 13 + 211 + 375 + 65 = 666.

It is not a de Polignac number, because 21321137565 - 2⁴ = 21321137549 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 59212 + ... + 214821.

It is an arithmetic number, because the mean of its divisors is an integer number (498741880).

Almost surely, 2^21321137565 is an apocalyptic number.

It is an amenable number.

21321137565 is an abundant number, since it is smaller than the sum of its proper divisors (26558082915).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21321137565 is a wasteful number, since it uses less digits than its factorization.

21321137565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 274083 (or 274080 counting only the distinct ones).

The product of its digits is 37800, while the sum is 36.

Adding to 21321137565 its reverse (56573112312), we get a palindrome (77894249877).

The spelling of 21321137565 in words is "twenty-one billion, three hundred twenty-one million, one hundred thirty-seven thousand, five hundred sixty-five".