21811279 has 4 divisors (see below), whose sum is σ = 24927184. Its totient is φ = 18695376.

The previous prime is 21811261. The next prime is 21811351. The reversal of 21811279 is 97211812.

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

It is not a de Polignac number, because 21811279 - 2¹¹ = 21809231 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21811279.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811079) 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, 1557942 + ... + 1557955.

It is an arithmetic number, because the mean of its divisors is an integer number (6231796).

Almost surely, 2^21811279 is an apocalyptic number.

21811279 is a deficient number, since it is larger than the sum of its proper divisors (3115905).

21811279 is an equidigital number, since it uses as much as digits as its factorization.

21811279 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3115904.

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

The square root of 21811279 is about 4670.2547039749. The cubic root of 21811279 is about 279.4004134019.

The spelling of 21811279 in words is "twenty-one million, eight hundred eleven thousand, two hundred seventy-nine".