21985618 has 4 divisors (see below), whose sum is σ = 32978430. Its totient is φ = 10992808.

The previous prime is 21985609. The next prime is 21985637. The reversal of 21985618 is 81658912.

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., 17114769 + 4870849 = 4137^2 + 2207^2 .

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5496403 + ... + 5496406.

Almost surely, 2^21985618 is an apocalyptic number.

21985618 is a deficient number, since it is larger than the sum of its proper divisors (10992812).

21985618 is a wasteful number, since it uses less digits than its factorization.

21985618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10992811.

The product of its digits is 34560, while the sum is 40.

The square root of 21985618 is about 4688.8823828286. The cubic root of 21985618 is about 280.1428607711.

The spelling of 21985618 in words is "twenty-one million, nine hundred eighty-five thousand, six hundred eighteen".