21395522581 has 4 divisors (see below), whose sum is σ = 21411175392. Its totient is φ = 21379869772.

The previous prime is 21395522569. The next prime is 21395522609. The reversal of 21395522581 is 18522559312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21395522581 - 2⁵ = 21395522549 is a prime.

It is a super-2 number, since 2×21395522581² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21395522881) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 7824355 + ... + 7827088.

It is an arithmetic number, because the mean of its divisors is an integer number (5352793848).

Almost surely, 2^21395522581 is an apocalyptic number.

It is an amenable number.

21395522581 is a deficient number, since it is larger than the sum of its proper divisors (15652811).

21395522581 is a wasteful number, since it uses less digits than its factorization.

21395522581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15652810.

The product of its digits is 216000, while the sum is 43.

The spelling of 21395522581 in words is "twenty-one billion, three hundred ninety-five million, five hundred twenty-two thousand, five hundred eighty-one".