21819618 has 30 divisors (see below), whose sum is σ = 49025691. Its totient is φ = 7253388.

The previous prime is 21819601. The next prime is 21819643. The reversal of 21819618 is 81691812.

21819618 is a `hidden beast` number, since 21 + 8 + 19 + 618 = 666.

It can be written as a sum of positive squares in only one way, i.e., 10909809 + 10909809 = 3303^2 + 3303^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=3303.

It is an unprimeable number.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 59271 + ... + 59637.

Almost surely, 2^21819618 is an apocalyptic number.

21819618 is an abundant number, since it is smaller than the sum of its proper divisors (27206073).

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

21819618 is an frugal number, since it uses more digits than its factorization.

21819618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 748 (or 372 counting only the distinct ones).

The product of its digits is 6912, while the sum is 36.

The square root of 21819618 is about 4671.1473965183. The cubic root of 21819618 is about 279.4360161311.

It can be divided in two parts, 218 and 19618, that multiplied together give a palindrome (4276724).

The spelling of 21819618 in words is "twenty-one million, eight hundred nineteen thousand, six hundred eighteen".