21885991 has 4 divisors (see below), whose sum is σ = 22257000. Its totient is φ = 21514984.

The previous prime is 21885961. The next prime is 21886027. The reversal of 21885991 is 19958812.

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 21885991 - 2⁵ = 21885959 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 (21885961) 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, 185416 + ... + 185533.

It is an arithmetic number, because the mean of its divisors is an integer number (5564250).

Almost surely, 2^21885991 is an apocalyptic number.

21885991 is a deficient number, since it is larger than the sum of its proper divisors (371009).

21885991 is an equidigital number, since it uses as much as digits as its factorization.

21885991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 371008.

The product of its digits is 51840, while the sum is 43.

The square root of 21885991 is about 4678.2465732366. The cubic root of 21885991 is about 279.7190677164.

The spelling of 21885991 in words is "twenty-one million, eight hundred eighty-five thousand, nine hundred ninety-one".