21907009 has 4 divisors (see below), whose sum is σ = 21916804. Its totient is φ = 21897216.

The previous prime is 21907007. The next prime is 21907013. The reversal of 21907009 is 90070912.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 2958400 + 18948609 = 1720^2 + 4353^2 .

It is a cyclic number.

It is not a de Polignac number, because 21907009 - 2¹ = 21907007 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21907007) 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, 289 + ... + 6625.

It is an arithmetic number, because the mean of its divisors is an integer number (5479201).

It is a Poulet number, since it divides 2^21907008-1.

Almost surely, 2^21907009 is an apocalyptic number.

It is an amenable number.

21907009 is a deficient number, since it is larger than the sum of its proper divisors (9795).

21907009 is an equidigital number, since it uses as much as digits as its factorization.

21907009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9794.

The product of its (nonzero) digits is 1134, while the sum is 28.

The square root of 21907009 is about 4680.4923886275. The cubic root of 21907009 is about 279.8085809028.

The spelling of 21907009 in words is "twenty-one million, nine hundred seven thousand, nine".