21728231 has 16 divisors (see below), whose sum is σ = 25482048. Its totient is φ = 18144000.

The previous prime is 21728197. The next prime is 21728233. The reversal of 21728231 is 13282712.

It is not a de Polignac number, because 21728231 - 2²² = 17533927 is a prime.

It is a super-2 number, since 2×21728231² = 944232044778722, which contains 22 as substring.

It is a Smith number, since the sum of its digits (26) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21728231.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728233) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 51401 + ... + 51821.

It is an arithmetic number, because the mean of its divisors is an integer number (1592628).

Almost surely, 2^21728231 is an apocalyptic number.

21728231 is a deficient number, since it is larger than the sum of its proper divisors (3753817).

21728231 is a wasteful number, since it uses less digits than its factorization.

21728231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 602.

The product of its digits is 1344, while the sum is 26.

The square root of 21728231 is about 4661.3550604947. The cubic root of 21728231 is about 279.0453500448.

The spelling of 21728231 in words is "twenty-one million, seven hundred twenty-eight thousand, two hundred thirty-one".