21821724 has 60 divisors (see below), whose sum is σ = 58300704. Its totient is φ = 7114176.

The previous prime is 21821707. The next prime is 21821729. The reversal of 21821724 is 42712812.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821729) 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 in 19 ways as a sum of consecutive naturals, for example, 14512 + ... + 15944.

Almost surely, 2^21821724 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21821724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29150352).

21821724 is an abundant number, since it is smaller than the sum of its proper divisors (36478980).

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

21821724 is a wasteful number, since it uses less digits than its factorization.

21821724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1496 (or 1485 counting only the distinct ones).

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

The square root of 21821724 is about 4671.3728174917. The cubic root of 21821724 is about 279.4450061039.

The spelling of 21821724 in words is "twenty-one million, eight hundred twenty-one thousand, seven hundred twenty-four".