21921871 has 4 divisors (see below), whose sum is σ = 22514392. Its totient is φ = 21329352.

The previous prime is 21921869. The next prime is 21921899. The reversal of 21921871 is 17812912.

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 21921871 - 2¹ = 21921869 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 (21921811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 296205 + ... + 296278.

It is an arithmetic number, because the mean of its divisors is an integer number (5628598).

Almost surely, 2^21921871 is an apocalyptic number.

21921871 is a deficient number, since it is larger than the sum of its proper divisors (592521).

21921871 is an equidigital number, since it uses as much as digits as its factorization.

21921871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 592520.

The product of its digits is 2016, while the sum is 31.

The square root of 21921871 is about 4682.0797729214. The cubic root of 21921871 is about 279.8718418602.

The spelling of 21921871 in words is "twenty-one million, nine hundred twenty-one thousand, eight hundred seventy-one".