21206618 has 8 divisors (see below), whose sum is σ = 32013012. Its totient is φ = 10535616.

The previous prime is 21206617. The next prime is 21206623. The reversal of 21206618 is 81660212.

It can be written as a sum of positive squares in 2 ways, for example, as 18258529 + 2948089 = 4273^2 + 1717^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21206617) 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, 33455 + ... + 34082.

Almost surely, 2^21206618 is an apocalyptic number.

21206618 is a deficient number, since it is larger than the sum of its proper divisors (10806394).

21206618 is a wasteful number, since it uses less digits than its factorization.

21206618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67696.

The product of its (nonzero) digits is 1152, while the sum is 26.

The square root of 21206618 is about 4605.0643860863. The cubic root of 21206618 is about 276.7942970107.

The spelling of 21206618 in words is "twenty-one million, two hundred six thousand, six hundred eighteen".