21728205 has 24 divisors (see below), whose sum is σ = 38004408. Its totient is φ = 11483136.

The previous prime is 21728197. The next prime is 21728233. The reversal of 21728205 is 50282712.

It can be written as a sum of positive squares in 4 ways, for example, as 328329 + 21399876 = 573^2 + 4626^2 .

It is not a de Polignac number, because 21728205 - 2³ = 21728197 is a prime.

It is a super-2 number, since 2×21728205² = 944229785044050, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2949 + ... + 7221.

It is an arithmetic number, because the mean of its divisors is an integer number (1583517).

Almost surely, 2^21728205 is an apocalyptic number.

It is an amenable number.

21728205 is a deficient number, since it is larger than the sum of its proper divisors (16276203).

21728205 is a wasteful number, since it uses less digits than its factorization.

21728205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4397 (or 4394 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21728205 is about 4661.3522716053. The cubic root of 21728205 is about 279.0452387429.

The spelling of 21728205 in words is "twenty-one million, seven hundred twenty-eight thousand, two hundred five".