21099409 has 4 divisors (see below), whose sum is σ = 21388516. Its totient is φ = 20810304.

The previous prime is 21099391. The next prime is 21099413. The reversal of 21099409 is 90499012.

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 9437184 + 11662225 = 3072^2 + 3415^2 .

It is a cyclic number.

It is not a de Polignac number, because 21099409 - 2¹⁵ = 21066641 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21099469) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 144444 + ... + 144589.

It is an arithmetic number, because the mean of its divisors is an integer number (5347129).

Almost surely, 2^21099409 is an apocalyptic number.

It is an amenable number.

21099409 is a deficient number, since it is larger than the sum of its proper divisors (289107).

21099409 is an equidigital number, since it uses as much as digits as its factorization.

21099409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 289106.

The product of its (nonzero) digits is 5832, while the sum is 34.

The square root of 21099409 is about 4593.4093002910. The cubic root of 21099409 is about 276.3270688516.

The spelling of 21099409 in words is "twenty-one million, ninety-nine thousand, four hundred nine".