21820618 has 4 divisors (see below), whose sum is σ = 32730930. Its totient is φ = 10910308.

The previous prime is 21820613. The next prime is 21820633. The reversal of 21820618 is 81602812.

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., 21557449 + 263169 = 4643^2 + 513^2 .

It is a super-2 number, since 2×21820618² = 952278739803848, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21820613) 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 as a sum of consecutive naturals, namely, 5455153 + ... + 5455156.

Almost surely, 2^21820618 is an apocalyptic number.

21820618 is a deficient number, since it is larger than the sum of its proper divisors (10910312).

21820618 is a wasteful number, since it uses less digits than its factorization.

21820618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10910311.

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 21820618 is about 4671.2544353739. The cubic root of 21820618 is about 279.4402849462.

The spelling of 21820618 in words is "twenty-one million, eight hundred twenty thousand, six hundred eighteen".