21528905 has 4 divisors (see below), whose sum is σ = 25834692. Its totient is φ = 17223120.

The previous prime is 21528893. The next prime is 21528929. The reversal of 21528905 is 50982512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4048144 + 17480761 = 2012^2 + 4181^2 .

It is not a de Polignac number, because 21528905 - 2⁴ = 21528889 is a prime.

It is a Duffinian number.

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, 2152886 + ... + 2152895.

It is an arithmetic number, because the mean of its divisors is an integer number (6458673).

Almost surely, 2^21528905 is an apocalyptic number.

It is an amenable number.

21528905 is a deficient number, since it is larger than the sum of its proper divisors (4305787).

21528905 is an equidigital number, since it uses as much as digits as its factorization.

21528905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4305786.

The product of its (nonzero) digits is 7200, while the sum is 32.

The square root of 21528905 is about 4639.9251071542. The cubic root of 21528905 is about 278.1894443940.

It can be divided in two parts, 215 and 28905, that multiplied together give a triangular number (6214575 = T₃₅₂₅).

The spelling of 21528905 in words is "twenty-one million, five hundred twenty-eight thousand, nine hundred five".