21000000009 has 24 divisors (see below), whose sum is σ = 28515142240. Its totient is φ = 13744406592.

The previous prime is 20999999981. The next prime is 21000000019. The reversal of 21000000009 is 90000000012.

It is a happy number.

It is not a de Polignac number, because 21000000009 - 2²¹ = 20997902857 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20999999940 and 21000000003.

It is not an unprimeable number, because it can be changed into a prime (21000000019) 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, 41749252 + ... + 41749754.

Almost surely, 2^21000000009 is an apocalyptic number.

It is an amenable number.

21000000009 is a deficient number, since it is larger than the sum of its proper divisors (7515142231).

21000000009 is an frugal number, since it uses more digits than its factorization.

21000000009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1461 (or 958 counting only the distinct ones).

The product of its (nonzero) digits is 18, while the sum is 12.

The spelling of 21000000009 in words is "twenty-one billion, nine", and thus it is an aban number and an uban number.