21115609 has 4 divisors (see below), whose sum is σ = 21156660. Its totient is φ = 21074560.

The previous prime is 21115603. The next prime is 21115651. The reversal of 21115609 is 90651112.

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 14040009 + 7075600 = 3747^2 + 2660^2 .

It is a cyclic number.

It is not a de Polignac number, because 21115609 - 2¹³ = 21107417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21115603) 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, 19744 + ... + 20785.

It is an arithmetic number, because the mean of its divisors is an integer number (5289165).

Almost surely, 2^21115609 is an apocalyptic number.

It is an amenable number.

21115609 is a deficient number, since it is larger than the sum of its proper divisors (41051).

21115609 is an equidigital number, since it uses as much as digits as its factorization.

21115609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41050.

The product of its (nonzero) digits is 540, while the sum is 25.

The square root of 21115609 is about 4595.1723580297. The cubic root of 21115609 is about 276.3977715164.

The spelling of 21115609 in words is "twenty-one million, one hundred fifteen thousand, six hundred nine".