21003009 has 4 divisors (see below), whose sum is σ = 28004016. Its totient is φ = 14002004.

The previous prime is 21003001. The next prime is 21003011. The reversal of 21003009 is 90030012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21003009 - 2³ = 21003001 is a prime.

It is a super-2 number, since 2×21003009² = 882252774108162, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21003001) 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, 3500499 + ... + 3500504.

It is an arithmetic number, because the mean of its divisors is an integer number (7001004).

Almost surely, 2^21003009 is an apocalyptic number.

It is an amenable number.

21003009 is a deficient number, since it is larger than the sum of its proper divisors (7001007).

21003009 is an equidigital number, since it uses as much as digits as its factorization.

21003009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7001006.

The product of its (nonzero) digits is 54, while the sum is 15.

The square root of 21003009 is about 4582.9039920121. The cubic root of 21003009 is about 275.9055941562.

The spelling of 21003009 in words is "twenty-one million, three thousand, nine".