21750728 has 8 divisors (see below), whose sum is σ = 40782630. Its totient is φ = 10875360.

The previous prime is 21750721. The next prime is 21750737. The reversal of 21750728 is 82705712.

It can be written as a sum of positive squares in only one way, i.e., 13118884 + 8631844 = 3622^2 + 2938^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a junction number, because it is equal to n+sod(n) for n = 21750694 and 21750703.

It is not an unprimeable number, because it can be changed into a prime (21750721) 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 as a sum of consecutive naturals, namely, 1359413 + ... + 1359428.

Almost surely, 2^21750728 is an apocalyptic number.

It is an amenable number.

21750728 is a deficient number, since it is larger than the sum of its proper divisors (19031902).

21750728 is a wasteful number, since it uses less digits than its factorization.

21750728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2718847 (or 2718843 counting only the distinct ones).

The product of its (nonzero) digits is 7840, while the sum is 32.

The square root of 21750728 is about 4663.7675756838. The cubic root of 21750728 is about 279.1416229211.

The spelling of 21750728 in words is "twenty-one million, seven hundred fifty thousand, seven hundred twenty-eight".