21559971 has 4 divisors (see below), whose sum is σ = 28746632. Its totient is φ = 14373312.

The previous prime is 21559949. The next prime is 21559991. The reversal of 21559971 is 17995512.

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

It is not a de Polignac number, because 21559971 - 2⁵ = 21559939 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21559991) 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, 3593326 + ... + 3593331.

It is an arithmetic number, because the mean of its divisors is an integer number (7186658).

Almost surely, 2^21559971 is an apocalyptic number.

21559971 is a deficient number, since it is larger than the sum of its proper divisors (7186661).

21559971 is an equidigital number, since it uses as much as digits as its factorization.

21559971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7186660.

The product of its digits is 28350, while the sum is 39.

The square root of 21559971 is about 4643.2715837004. The cubic root of 21559971 is about 278.3231883028.

The spelling of 21559971 in words is "twenty-one million, five hundred fifty-nine thousand, nine hundred seventy-one".