21729928 has 16 divisors (see below), whose sum is σ = 44447760. Its totient is φ = 9877200.

The previous prime is 21729919. The next prime is 21729931. The reversal of 21729928 is 82992712.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 123378 + ... + 123553.

It is an arithmetic number, because the mean of its divisors is an integer number (2777985).

Almost surely, 2^21729928 is an apocalyptic number.

It is an amenable number.

21729928 is an abundant number, since it is smaller than the sum of its proper divisors (22717832).

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

21729928 is a wasteful number, since it uses less digits than its factorization.

21729928 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 246948 (or 246944 counting only the distinct ones).

The product of its digits is 36288, while the sum is 40.

The square root of 21729928 is about 4661.5370855545. The cubic root of 21729928 is about 279.0526144440.

It can be divided in two parts, 2172 and 9928, that added together give a square (12100 = 110²).

The spelling of 21729928 in words is "twenty-one million, seven hundred twenty-nine thousand, nine hundred twenty-eight".