21818913 has 4 divisors (see below), whose sum is σ = 29091888. Its totient is φ = 14545940.

The previous prime is 21818899. The next prime is 21818921. The reversal of 21818913 is 31981812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21818913 - 2¹² = 21814817 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21818963) 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, 3636483 + ... + 3636488.

It is an arithmetic number, because the mean of its divisors is an integer number (7272972).

Almost surely, 2^21818913 is an apocalyptic number.

It is an amenable number.

21818913 is a deficient number, since it is larger than the sum of its proper divisors (7272975).

21818913 is an equidigital number, since it uses as much as digits as its factorization.

21818913 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7272974.

The product of its digits is 3456, while the sum is 33.

The square root of 21818913 is about 4671.0719326510. The cubic root of 21818913 is about 279.4330065380.

The spelling of 21818913 in words is "twenty-one million, eight hundred eighteen thousand, nine hundred thirteen".