21921724 has 24 divisors (see below), whose sum is σ = 42190848. Its totient is φ = 9883440.

The previous prime is 21921703. The next prime is 21921733. The reversal of 21921724 is 42712912.

It is a junction number, because it is equal to n+sod(n) for n = 21921692 and 21921701.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3627 + ... + 7549.

It is an arithmetic number, because the mean of its divisors is an integer number (1757952).

Almost surely, 2^21921724 is an apocalyptic number.

It is an amenable number.

21921724 is a deficient number, since it is larger than the sum of its proper divisors (20269124).

21921724 is a wasteful number, since it uses less digits than its factorization.

21921724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4065 (or 4063 counting only the distinct ones).

The product of its digits is 2016, while the sum is 28.

The square root of 21921724 is about 4682.0640747431. The cubic root of 21921724 is about 279.8712162863.

It can be divided in two parts, 2192 and 1724, that added together give a triangular number (3916 = T₈₈).

The spelling of 21921724 in words is "twenty-one million, nine hundred twenty-one thousand, seven hundred twenty-four".