21591571 has 4 divisors (see below), whose sum is σ = 21607272. Its totient is φ = 21575872.

The previous prime is 21591553. The next prime is 21591587. The reversal of 21591571 is 17519512.

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 21591571 - 2⁵ = 21591539 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21591541) 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, 5566 + ... + 8611.

It is an arithmetic number, because the mean of its divisors is an integer number (5401818).

Almost surely, 2^21591571 is an apocalyptic number.

21591571 is a deficient number, since it is larger than the sum of its proper divisors (15701).

21591571 is a wasteful number, since it uses less digits than its factorization.

21591571 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15700.

The product of its digits is 3150, while the sum is 31.

The square root of 21591571 is about 4646.6731109472. The cubic root of 21591571 is about 278.4590994218.

The spelling of 21591571 in words is "twenty-one million, five hundred ninety-one thousand, five hundred seventy-one".