21724812 has 18 divisors (see below), whose sum is σ = 54915588. Its totient is φ = 7241592.

The previous prime is 21724783. The next prime is 21724819. The reversal of 21724812 is 21842712.

It is a tau number, because it is divible by the number of its divisors (18).

It is not an unprimeable number, because it can be changed into a prime (21724819) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 301698 + ... + 301769.

It is an arithmetic number, because the mean of its divisors is an integer number (3050866).

Almost surely, 2^21724812 is an apocalyptic number.

It is an amenable number.

21724812 is an abundant number, since it is smaller than the sum of its proper divisors (33190776).

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

21724812 is a wasteful number, since it uses less digits than its factorization.

21724812 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 603477 (or 603472 counting only the distinct ones).

The product of its digits is 1792, while the sum is 27.

The square root of 21724812 is about 4660.9883072155. The cubic root of 21724812 is about 279.0307130794.

The spelling of 21724812 in words is "twenty-one million, seven hundred twenty-four thousand, eight hundred twelve".