21618811 has 4 divisors (see below), whose sum is σ = 22316224. Its totient is φ = 20921400.

The previous prime is 21618803. The next prime is 21618847. The reversal of 21618811 is 11881612.

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 21618811 - 2³ = 21618803 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 21618811.

It is not an unprimeable number, because it can be changed into a prime (21618511) 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, 348660 + ... + 348721.

It is an arithmetic number, because the mean of its divisors is an integer number (5579056).

Almost surely, 2^21618811 is an apocalyptic number.

21618811 is a deficient number, since it is larger than the sum of its proper divisors (697413).

21618811 is an equidigital number, since it uses as much as digits as its factorization.

21618811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 697412.

The product of its digits is 768, while the sum is 28.

The square root of 21618811 is about 4649.6033164131. The cubic root of 21618811 is about 278.5761518626.

The spelling of 21618811 in words is "twenty-one million, six hundred eighteen thousand, eight hundred eleven".