21724778 has 16 divisors (see below), whose sum is σ = 33064416. Its totient is φ = 10704720.

The previous prime is 21724757. The next prime is 21724783. The reversal of 21724778 is 87742712.

It is a happy number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74000 + ... + 74292.

It is an arithmetic number, because the mean of its divisors is an integer number (2066526).

Almost surely, 2^21724778 is an apocalyptic number.

21724778 is a deficient number, since it is larger than the sum of its proper divisors (11339638).

21724778 is a wasteful number, since it uses less digits than its factorization.

21724778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 709.

The product of its digits is 43904, while the sum is 38.

The square root of 21724778 is about 4660.9846599190. The cubic root of 21724778 is about 279.0305675154.

The spelling of 21724778 in words is "twenty-one million, seven hundred twenty-four thousand, seven hundred seventy-eight".