21010009 has 4 divisors (see below), whose sum is σ = 21032704. Its totient is φ = 20987316.

The previous prime is 21009997. The next prime is 21010013. The reversal of 21010009 is 90001012.

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 a de Polignac number, because none of the positive numbers 2^k-21010009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21010049) 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, 9897 + ... + 11830.

It is an arithmetic number, because the mean of its divisors is an integer number (5258176).

Almost surely, 2^21010009 is an apocalyptic number.

It is an amenable number.

21010009 is a deficient number, since it is larger than the sum of its proper divisors (22695).

21010009 is an equidigital number, since it uses as much as digits as its factorization.

21010009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22694.

The product of its (nonzero) digits is 18, while the sum is 13.

The square root of 21010009 is about 4583.6676362930. The cubic root of 21010009 is about 275.9362425367.

The spelling of 21010009 in words is "twenty-one million, ten thousand, nine".