21497591809 has 4 divisors (see below), whose sum is σ = 21498363904. Its totient is φ = 21496819716.

The previous prime is 21497591779. The next prime is 21497591821. The reversal of 21497591809 is 90819579412.

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 21497591809 - 2⁵ = 21497591777 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21497591809.

It is not an unprimeable number, because it can be changed into a prime (21497591839) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 342657 + ... + 400510.

It is an arithmetic number, because the mean of its divisors is an integer number (5374590976).

Almost surely, 2^21497591809 is an apocalyptic number.

It is an amenable number.

21497591809 is a deficient number, since it is larger than the sum of its proper divisors (772095).

21497591809 is an equidigital number, since it uses as much as digits as its factorization.

21497591809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 772094.

The product of its (nonzero) digits is 1632960, while the sum is 55.

The spelling of 21497591809 in words is "twenty-one billion, four hundred ninety-seven million, five hundred ninety-one thousand, eight hundred nine".