21730728 has 32 divisors (see below), whose sum is σ = 54986400. Its totient is φ = 7155648.

The previous prime is 21730727. The next prime is 21730739. The reversal of 21730728 is 82703712.

It is a junction number, because it is equal to n+sod(n) for n = 21730695 and 21730704.

It is not an unprimeable number, because it can be changed into a prime (21730727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3463 + ... + 7446.

It is an arithmetic number, because the mean of its divisors is an integer number (1718325).

Almost surely, 2^21730728 is an apocalyptic number.

It is an amenable number.

21730728 is an abundant number, since it is smaller than the sum of its proper divisors (33255672).

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

21730728 is a wasteful number, since it uses less digits than its factorization.

21730728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11001 (or 10997 counting only the distinct ones).

The product of its (nonzero) digits is 4704, while the sum is 30.

The square root of 21730728 is about 4661.6228933709. The cubic root of 21730728 is about 279.0560388970.

It can be divided in two parts, 2 and 1730728, that added together give a triangular number (1730730 = T₁₈₆₀).

The spelling of 21730728 in words is "twenty-one million, seven hundred thirty thousand, seven hundred twenty-eight".