21493591 has 4 divisors (see below), whose sum is σ = 24564112. Its totient is φ = 18423072.

The previous prime is 21493583. The next prime is 21493603. The reversal of 21493591 is 19539412.

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 21493591 - 2³ = 21493583 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21493531) 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, 1535250 + ... + 1535263.

It is an arithmetic number, because the mean of its divisors is an integer number (6141028).

Almost surely, 2^21493591 is an apocalyptic number.

21493591 is a deficient number, since it is larger than the sum of its proper divisors (3070521).

21493591 is an equidigital number, since it uses as much as digits as its factorization.

21493591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3070520.

The product of its digits is 9720, while the sum is 34.

The square root of 21493591 is about 4636.1180959937. The cubic root of 21493591 is about 278.0372558458.

The spelling of 21493591 in words is "twenty-one million, four hundred ninety-three thousand, five hundred ninety-one".