21591497 has 4 divisors (see below), whose sum is σ = 21601296. Its totient is φ = 21581700.

The previous prime is 21591491. The next prime is 21591523. The reversal of 21591497 is 79419512.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21591497 - 2⁴ = 21591481 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 21591497.

It is not an unprimeable number, because it can be changed into a prime (21591491) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 122 + ... + 6572.

It is an arithmetic number, because the mean of its divisors is an integer number (5400324).

Almost surely, 2^21591497 is an apocalyptic number.

It is an amenable number.

21591497 is a deficient number, since it is larger than the sum of its proper divisors (9799).

21591497 is an equidigital number, since it uses as much as digits as its factorization.

21591497 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9798.

The product of its digits is 22680, while the sum is 38.

The square root of 21591497 is about 4646.6651482542. The cubic root of 21591497 is about 278.4587813039.

The spelling of 21591497 in words is "twenty-one million, five hundred ninety-one thousand, four hundred ninety-seven".