21591502079 has 4 divisors (see below), whose sum is σ = 24676002384. Its totient is φ = 18507001776.

The previous prime is 21591502061. The next prime is 21591502091. The reversal of 21591502079 is 97020519512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21591502079 - 2²⁴ = 21574724863 is a prime.

It is a super-2 number, since 2×21591502079² (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 (21591502019) 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, 1542250142 + ... + 1542250155.

It is an arithmetic number, because the mean of its divisors is an integer number (6169000596).

Almost surely, 2^21591502079 is an apocalyptic number.

21591502079 is a deficient number, since it is larger than the sum of its proper divisors (3084500305).

21591502079 is an equidigital number, since it uses as much as digits as its factorization.

21591502079 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3084500304.

The product of its (nonzero) digits is 56700, while the sum is 41.

The spelling of 21591502079 in words is "twenty-one billion, five hundred ninety-one million, five hundred two thousand, seventy-nine".