21724221 has 8 divisors (see below), whose sum is σ = 29090880. Its totient is φ = 14420192.

The previous prime is 21724207. The next prime is 21724229. The reversal of 21724221 is 12242712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21724221 - 2⁵ = 21724189 is a prime.

It is a super-3 number, since 3×21724221³ (a number of 23 digits) contains 333 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14841 + ... + 16238.

It is an arithmetic number, because the mean of its divisors is an integer number (3636360).

Almost surely, 2^21724221 is an apocalyptic number.

It is an amenable number.

21724221 is a deficient number, since it is larger than the sum of its proper divisors (7366659).

21724221 is a wasteful number, since it uses less digits than its factorization.

21724221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31315.

The product of its digits is 448, while the sum is 21.

The square root of 21724221 is about 4660.9249082130. The cubic root of 21724221 is about 279.0281828136.

Adding to 21724221 its reverse (12242712), we get a palindrome (33966933).

It can be divided in two parts, 21724 and 221, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21724221 in words is "twenty-one million, seven hundred twenty-four thousand, two hundred twenty-one".