21540109 has 4 divisors (see below), whose sum is σ = 21572604. Its totient is φ = 21507616.

The previous prime is 21540083. The next prime is 21540157. The reversal of 21540109 is 90104512.

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 20675209 + 864900 = 4547^2 + 930^2 .

It is a cyclic number.

It is not a de Polignac number, because 21540109 - 2¹¹ = 21538061 is a prime.

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 21540109.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21540209) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15232 + ... + 16585.

It is an arithmetic number, because the mean of its divisors is an integer number (5393151).

Almost surely, 2^21540109 is an apocalyptic number.

It is an amenable number.

21540109 is a deficient number, since it is larger than the sum of its proper divisors (32495).

21540109 is an equidigital number, since it uses as much as digits as its factorization.

21540109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32494.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21540109 is about 4641.1322971878. The cubic root of 21540109 is about 278.2376941618.

The spelling of 21540109 in words is "twenty-one million, five hundred forty thousand, one hundred nine".