21728565 has 24 divisors (see below), whose sum is σ = 38584728. Its totient is φ = 11304960.

The previous prime is 21728563. The next prime is 21728573. The reversal of 21728565 is 56582712.

It is a happy number.

21728565 is a `hidden beast` number, since 21 + 72 + 8 + 565 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 439569 + 21288996 = 663^2 + 4614^2 .

It is not a de Polignac number, because 21728565 - 2¹ = 21728563 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4044 + ... + 7733.

It is an arithmetic number, because the mean of its divisors is an integer number (1607697).

Almost surely, 2^21728565 is an apocalyptic number.

It is an amenable number.

21728565 is a deficient number, since it is larger than the sum of its proper divisors (16856163).

21728565 is a wasteful number, since it uses less digits than its factorization.

21728565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11829 (or 11826 counting only the distinct ones).

The product of its digits is 33600, while the sum is 36.

The square root of 21728565 is about 4661.3908868491. The cubic root of 21728565 is about 279.0467798386.

It can be divided in two parts, 217 and 28565, that added together give a palindrome (28782).

The spelling of 21728565 in words is "twenty-one million, seven hundred twenty-eight thousand, five hundred sixty-five".