21557591 has 16 divisors (see below), whose sum is σ = 24261120. Its totient is φ = 18988320.

The previous prime is 21557579. The next prime is 21557593. The reversal of 21557591 is 19575512.

It is a cyclic number.

It is not a de Polignac number, because 21557591 - 2¹⁰ = 21556567 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 (21557593) 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 15 ways as a sum of consecutive naturals, for example, 59870 + ... + 60228.

It is an arithmetic number, because the mean of its divisors is an integer number (1516320).

Almost surely, 2^21557591 is an apocalyptic number.

21557591 is a deficient number, since it is larger than the sum of its proper divisors (2703529).

21557591 is a wasteful number, since it uses less digits than its factorization.

21557591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 526.

The product of its digits is 15750, while the sum is 35.

The square root of 21557591 is about 4643.0152918120. The cubic root of 21557591 is about 278.3129465827.

The spelling of 21557591 in words is "twenty-one million, five hundred fifty-seven thousand, five hundred ninety-one".