21684571 has 4 divisors (see below), whose sum is σ = 22960152. Its totient is φ = 20408992.

The previous prime is 21684557. The next prime is 21684589. The reversal of 21684571 is 17548612.

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 21684571 - 2¹⁵ = 21651803 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21684511) 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 3 ways as a sum of consecutive naturals, for example, 637765 + ... + 637798.

It is an arithmetic number, because the mean of its divisors is an integer number (5740038).

Almost surely, 2^21684571 is an apocalyptic number.

21684571 is a deficient number, since it is larger than the sum of its proper divisors (1275581).

21684571 is a wasteful number, since it uses less digits than its factorization.

21684571 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1275580.

The product of its digits is 13440, while the sum is 34.

The square root of 21684571 is about 4656.6695180139. The cubic root of 21684571 is about 278.8583231729.

The spelling of 21684571 in words is "twenty-one million, six hundred eighty-four thousand, five hundred seventy-one".