21813844 has 54 divisors (see below), whose sum is σ = 43920366. Its totient is φ = 9472320.

The previous prime is 21813833. The next prime is 21813877. The reversal of 21813844 is 44831812.

It can be written as a sum of positive squares in 3 ways, for example, as 1904400 + 19909444 = 1380^2 + 4462^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 357574 + ... + 357634.

Almost surely, 2^21813844 is an apocalyptic number.

It is an amenable number.

21813844 is an abundant number, since it is smaller than the sum of its proper divisors (22106522).

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

21813844 is a wasteful number, since it uses less digits than its factorization.

21813844 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137 (or 99 counting only the distinct ones).

The product of its digits is 6144, while the sum is 31.

The square root of 21813844 is about 4670.5293061922. The cubic root of 21813844 is about 279.4113654414.

The spelling of 21813844 in words is "twenty-one million, eight hundred thirteen thousand, eight hundred forty-four".