21728722 has 4 divisors (see below), whose sum is σ = 32593086. Its totient is φ = 10864360.

The previous prime is 21728719. The next prime is 21728741. The reversal of 21728722 is 22782712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 18412681 + 3316041 = 4291^2 + 1821^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5432179 + ... + 5432182.

Almost surely, 2^21728722 is an apocalyptic number.

21728722 is a deficient number, since it is larger than the sum of its proper divisors (10864364).

21728722 is a wasteful number, since it uses less digits than its factorization.

21728722 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10864363.

The product of its digits is 6272, while the sum is 31.

The square root of 21728722 is about 4661.4077272858. The cubic root of 21728722 is about 279.0474519222.

The spelling of 21728722 in words is "twenty-one million, seven hundred twenty-eight thousand, seven hundred twenty-two".