21664618 has 4 divisors (see below), whose sum is σ = 32496930. Its totient is φ = 10832308.

The previous prime is 21664609. The next prime is 21664637. The reversal of 21664618 is 81646612.

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

It can be written as a sum of positive squares in only one way, i.e., 12766329 + 8898289 = 3573^2 + 2983^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5416153 + ... + 5416156.

Almost surely, 2^21664618 is an apocalyptic number.

21664618 is a deficient number, since it is larger than the sum of its proper divisors (10832312).

21664618 is a wasteful number, since it uses less digits than its factorization.

21664618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10832311.

The product of its digits is 13824, while the sum is 34.

The square root of 21664618 is about 4654.5266139533. The cubic root of 21664618 is about 278.7727666793.

The spelling of 21664618 in words is "twenty-one million, six hundred sixty-four thousand, six hundred eighteen".