21106609 has 4 divisors (see below), whose sum is σ = 21241204. Its totient is φ = 20972016.

The previous prime is 21106607. The next prime is 21106643. The reversal of 21106609 is 90660112.

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 10400625 + 10705984 = 3225^2 + 3272^2 .

It is a cyclic number.

It is not a de Polignac number, because 21106609 - 2¹ = 21106607 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21106607) 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, 67062 + ... + 67375.

It is an arithmetic number, because the mean of its divisors is an integer number (5310301).

Almost surely, 2^21106609 is an apocalyptic number.

It is an amenable number.

21106609 is a deficient number, since it is larger than the sum of its proper divisors (134595).

21106609 is a wasteful number, since it uses less digits than its factorization.

21106609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 134594.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 21106609 is about 4594.1929650375. The cubic root of 21106609 is about 276.3584967245.

The spelling of 21106609 in words is "twenty-one million, one hundred six thousand, six hundred nine".