21187728 has 30 divisors (see below), whose sum is σ = 59296614. Its totient is φ = 7062528.

The previous prime is 21187697. The next prime is 21187753. The reversal of 21187728 is 82778112.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 19079424 + 2108304 = 4368^2 + 1452^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21187692 and 21187701.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 73425 + ... + 73712.

Almost surely, 2^21187728 is an apocalyptic number.

It is an amenable number.

21187728 is an abundant number, since it is smaller than the sum of its proper divisors (38108886).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21187728 is a wasteful number, since it uses less digits than its factorization.

21187728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147151 (or 147142 counting only the distinct ones).

The product of its digits is 12544, while the sum is 36.

The square root of 21187728 is about 4603.0129263342. The cubic root of 21187728 is about 276.7120868640.

The spelling of 21187728 in words is "twenty-one million, one hundred eighty-seven thousand, seven hundred twenty-eight".