21042609 has 24 divisors (see below), whose sum is σ = 33406560. Its totient is φ = 11741184.

The previous prime is 21042601. The next prime is 21042629. The reversal of 21042609 is 90624012.

It is not a de Polignac number, because 21042609 - 2³ = 21042601 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21042601) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4657 + ... + 7985.

It is an arithmetic number, because the mean of its divisors is an integer number (1391940).

Almost surely, 2^21042609 is an apocalyptic number.

It is an amenable number.

21042609 is a deficient number, since it is larger than the sum of its proper divisors (12363951).

21042609 is a wasteful number, since it uses less digits than its factorization.

21042609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3389 (or 3382 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21042609 is about 4587.2223621708. Note that the first 3 decimals coincide. The cubic root of 21042609 is about 276.0788868181.

The spelling of 21042609 in words is "twenty-one million, forty-two thousand, six hundred nine".