21552591 has 4 divisors (see below), whose sum is σ = 28736792. Its totient is φ = 14368392.

The previous prime is 21552571. The next prime is 21552607. The reversal of 21552591 is 19525512.

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

It is not a de Polignac number, because 21552591 - 2¹⁸ = 21290447 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 (21552521) 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, 3592096 + ... + 3592101.

It is an arithmetic number, because the mean of its divisors is an integer number (7184198).

Almost surely, 2^21552591 is an apocalyptic number.

21552591 is a deficient number, since it is larger than the sum of its proper divisors (7184201).

21552591 is an equidigital number, since it uses as much as digits as its factorization.

21552591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7184200.

The product of its digits is 4500, while the sum is 30.

The square root of 21552591 is about 4642.4768173896. The cubic root of 21552591 is about 278.2914279085.

The spelling of 21552591 in words is "twenty-one million, five hundred fifty-two thousand, five hundred ninety-one".