21381618 has 16 divisors (see below), whose sum is σ = 42821280. Its totient is φ = 7117536.

The previous prime is 21381617. The next prime is 21381653. The reversal of 21381618 is 81618312.

It is a super-3 number, since 3×21381618³ (a number of 23 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21381611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3478 + ... + 7406.

It is an arithmetic number, because the mean of its divisors is an integer number (2676330).

Almost surely, 2^21381618 is an apocalyptic number.

21381618 is an abundant number, since it is smaller than the sum of its proper divisors (21439662).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21381618 is a wasteful number, since it uses less digits than its factorization.

21381618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4841.

The product of its digits is 2304, while the sum is 30.

The square root of 21381618 is about 4624.0261677460. The cubic root of 21381618 is about 277.5535940638.

The spelling of 21381618 in words is "twenty-one million, three hundred eighty-one thousand, six hundred eighteen".