21643571 has 4 divisors (see below), whose sum is σ = 21699600. Its totient is φ = 21587544.

The previous prime is 21643519. The next prime is 21643607. The reversal of 21643571 is 17534612.

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 21643571 - 2⁶ = 21643507 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21693571) 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, 27431 + ... + 28208.

It is an arithmetic number, because the mean of its divisors is an integer number (5424900).

Almost surely, 2^21643571 is an apocalyptic number.

21643571 is a deficient number, since it is larger than the sum of its proper divisors (56029).

21643571 is an equidigital number, since it uses as much as digits as its factorization.

21643571 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 56028.

The product of its digits is 5040, while the sum is 29.

The square root of 21643571 is about 4652.2651472159. The cubic root of 21643571 is about 278.6824622720.

The spelling of 21643571 in words is "twenty-one million, six hundred forty-three thousand, five hundred seventy-one".