21918609 has 24 divisors (see below), whose sum is σ = 34781760. Its totient is φ = 13239072.

The previous prime is 21918607. The next prime is 21918649. The reversal of 21918609 is 90681912.

21918609 = 41³ + 42³ + ... + 97³.

It is not a de Polignac number, because 21918609 - 2¹ = 21918607 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21918601) 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 23 ways as a sum of consecutive naturals, for example, 1147 + ... + 6719.

It is an arithmetic number, because the mean of its divisors is an integer number (1449240).

Almost surely, 2^21918609 is an apocalyptic number.

It is an amenable number.

21918609 is a deficient number, since it is larger than the sum of its proper divisors (12863151).

21918609 is a wasteful number, since it uses less digits than its factorization.

21918609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5621 (or 5618 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21918609 is about 4681.7314104933. The cubic root of 21918609 is about 279.8579594193.

The spelling of 21918609 in words is "twenty-one million, nine hundred eighteen thousand, six hundred nine".